I finally got perfect 1080i working under mythtv and my LG 44hm85 tv. Here is my xorg.conf if it helps anyone. I wish there was a way to shrink the screen size about 1/2 inch. Cutting off some of the text at the top and sides of the tv.

Section "ServerLayout"
Identifier "XFree86 Configured"
Screen 0 "Screen0" 0 0
InputDevice "Keyboard0" "CoreKeyboard"
# PS/2 Mouse not detected
# Serial Mouse not detected
InputDevice "USB Mouse" "CorePointer"
EndSection

Section "ServerFlags"
Option "AllowMouseOpenFail" "true"

EndSection

Section "Files"
RgbPath "/usr/share/X11/rgb"
ModulePath "/usr/lib/xorg/modules"
FontPath "/usr/share/fonts/X11/misc:unscaled"
FontPath "/usr/share/fonts/X11/75dpi:unscaled"
FontPath "/usr/share/fonts/X11/100dpi:unscaled"
FontPath "/usr/share/fonts/X11/Type1"
FontPath "/usr/share/fonts/X11/Speedo"
FontPath "/usr/share/fonts/X11/PEX"
# Additional fonts: Locale, Gimp, TTF...
FontPath "/usr/share/fonts/X11/cyrillic"
# FontPath "/usr/share/fonts/X11/latin2/75dpi"
# FontPath "/usr/share/fonts/X11/latin2/100dpi"
# True type and type1 fonts are also handled via xftlib, see /etc/X11/XftConfig!
FontPath "/var/lib/defoma/x-ttcidfont-conf.d/dirs/TrueType"
FontPath "/usr/share/fonts/truetype"
FontPath "/usr/share/fonts/latex-ttf-fonts"
EndSection

Section "Module"
# Comments: see http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=346408
Load "dbe" # Double Buffering Extension, very important.
# Load "dri" # This shouldn't be available choice if user has selected driver vga, vesa or nv.
Load "glx" # GLX Extension.
Load "freetype" # Freetype fonts.
Load "type1" # Type 1 fonts
Load "record" # Developer extension, usually not needed
# Load "extmod" # This is okay, but if you look into "man xorg.conf" you'll find option NOT to include DGA extension with extmod, and for a good reason.. DGA causes instability as it access videoram without consulting X about it.
SubSection "extmod"
Option "omit xfree86-dga"
EndSubSection
# Load "speedo" # Speedo fonts, this module doesn't exist in Xorg 7.0.17
# The following are deprecated/unstable/unneeded in Xorg 7.0
# Load "ddc" # ddc probing of monitor, this should be never present, as it gets automatically loaded.
# Load "GLcore" # This should be never present, as it gets automatically loaded.
# Load "bitmap" # Should be never present, as it gets automatically loaded. This is a font module, and loading it in xorg.conf makes X try to load it twice.
EndSection

Section "InputDevice"
Identifier "Keyboard0"
Driver "kbd"
Option "CoreKeyboard"
Option "XkbRules" "xorg"
Option "XkbModel" "pc105"
Option "XkbLayout" "us"

EndSection

Section "InputDevice"
Identifier "Serial Mouse"
Driver "mouse"
Option "Protocol" "Microsoft"
Option "Device" "/dev/ttyS0"
Option "Emulate3Buttons" "true"
Option "Emulate3Timeout" "70"
Option "SendCoreEvents" "true"
EndSection

Section "InputDevice"
Identifier "PS/2 Mouse"
Driver "mouse"
Option "Protocol" "auto"
Option "ZAxisMapping" "4 5"
Option "Device" "/dev/psaux"
Option "Emulate3Buttons" "true"
Option "Emulate3Timeout" "70"
Option "SendCoreEvents" "true"
EndSection

Section "InputDevice"
Identifier "USB Mouse"
Driver "mouse"
Option "Device" "/dev/input/mice"
Option "SendCoreEvents" "true"
Option "Protocol" "IMPS/2"
Option "ZAxisMapping" "4 5"
Option "Buttons" "5"
EndSection

# Auto-generated by KNOPPIX mkxf86config

Section "Monitor"
Identifier "Monitor0"
Option "DPMS" "true"
HorizSync 30 - 82 # DDC-probed
VertRefresh 56 - 76 # DDC-probed
Option "DPI" "100 x 100"
EndSection

Section "Device"
Option "RenderAccel" "True"
Option "BackingStore" "True"
# Option "MetaModes" "nvidia-auto-select"
Option "MetaModes" "1920x1080" #if you're using 1080i or 1080p
Option "ConnectedMonitor" "DFP-0"
# Option "TVStandard" "HD720p"
Option "TVStandard" "HD1080i"
Option "ModeValidation" "AllowNon60HzDFPModes, NoVertRefreshCheck, NoEdidMaxPClkCheck, NoHorizSyncCheck"
Option "UseEdidDPI" "False"
Option "XvmcUsesTextures" "True"
Identifier "Card0"
# The following line is auto-generated by KNOPPIX mkxf86config
Driver "nvidia"
VendorName "All"
BoardName "All"
# BusID "PCI:1:0:0"
EndSection




Section "Screen"
Identifier "Screen0"
Device "Card0"
Monitor "Monitor0"
DefaultColorDepth 24
SubSection "Display"
Depth 1
Modes "1280x1024" "1152x864" "1024x768" "800x600" "640x480"
EndSubSection
SubSection "Display"
Depth 4
Modes "1280x1024" "1152x864" "1024x768" "800x600" "640x480"
EndSubSection
SubSection "Display"
Depth 8
Modes "1280x1024" "1152x864" "1024x768" "800x600" "640x480"
EndSubSection
SubSection "Display"
Depth 15
Modes "1280x1024" "1152x864" "1024x768" "800x600" "640x480"
EndSubSection
SubSection "Display"
Depth 16
Modes "1280x1024" "1152x864" "1024x768" "800x600" "640x480"
EndSubSection
SubSection "Display"
Depth 24
Modes "1280x1024" "1152x864" "1024x768" "800x600" "640x480"
EndSubSection
SubSection "Display"
Depth 32
Modes "1280x1024" "1152x864" "1024x768" "800x600" "640x480"
EndSubSection
EndSection

Section "DRI"
Mode 0666
EndSection

(**) NVIDIA(0): Depth 24, (--) framebuffer bpp 32
(==) NVIDIA(0): RGB weight 888
(==) NVIDIA(0): Default visual is TrueColor
(==) NVIDIA(0): Using gamma correction (1.0, 1.0, 1.0)
(**) NVIDIA(0): Option "ConnectedMonitor" "DFP-0"
(**) NVIDIA(0): Option "TVStandard" "HD1080i"
(**) NVIDIA(0): Option "RenderAccel" "True"
(**) NVIDIA(0): Option "MetaModes" "1920x1080"
(**) NVIDIA(0): Option "XvMCUsesTextures" "True"
(**) NVIDIA(0): Option "UseEdidDpi" "False"
(**) NVIDIA(0): Option "DPI" "100 x 100"
(**) NVIDIA(0): Option "ModeValidation" "AllowNon60HzDFPModes, NoVertRefreshCheck, NoEdidMaxPClkCheck, NoHorizSyncCheck"
(**) NVIDIA(0): Enabling RENDER acceleration
(**) NVIDIA(0): TV Standard string: "HD1080i"
(**) NVIDIA(0): ConnectedMonitor string: "DFP-0"
(II) NVIDIA(0): NVIDIA GPU GeForce FX 5600 at PCI:1:0:0
(--) NVIDIA(0): VideoRAM: 262144 kBytes
(--) NVIDIA(0): VideoBIOS: 04.31.20.38.00
(II) NVIDIA(0): Detected AGP rate: 8X
(--) NVIDIA(0): Interlaced video modes are supported on this GPU
(--) NVIDIA(0): Connected display device(s) on GeForce FX 5600 at PCI:1:0:0:
(--) NVIDIA(0): LG TV (DFP-0)
(--) NVIDIA(0): LG TV (DFP-0): 140.4 MHz maximum pixel clock
(--) NVIDIA(0): LG TV (DFP-0): Internal Single Link TMDS
(II) NVIDIA(0): Mode Validation Overrides for LG TV (DFP-0):
(II) NVIDIA(0): AllowNon60HzDFPModes
(II) NVIDIA(0): NoEdidMaxPClkCheck
(II) NVIDIA(0): NoHorizSyncCheck
(II) NVIDIA(0): NoVertRefreshCheck
(WW) NVIDIA(0): Mode "1024x768" is too large for LG TV (DFP-0); discarding.
(WW) NVIDIA(0): Mode "1152x864" is too large for LG TV (DFP-0); discarding.
(WW) NVIDIA(0): Mode "1280x1024" is too large for LG TV (DFP-0); discarding.
(WW) NVIDIA(0): Mode "800x600" is too large for LG TV (DFP-0); discarding.
(WW) NVIDIA(0): Mode "800x600" is too large for LG TV (DFP-0); discarding.
(WW) NVIDIA(0): Mode "800x600" is too large for LG TV (DFP-0); discarding.
(WW) NVIDIA(0): Mode "800x600" is too large for LG TV (DFP-0); discarding.
(WW) NVIDIA(0): Mode "800x600" is too large for LG TV (DFP-0); discarding.
(WW) NVIDIA(0): Mode "896x672" is too large for LG TV (DFP-0); discarding.
(WW) NVIDIA(0): Mode "896x672" is too large for LG TV (DFP-0); discarding.
(WW) NVIDIA(0): Mode "928x696" is too large for LG TV (DFP-0); discarding.
(WW) NVIDIA(0): Mode "960x720" is too large for LG TV (DFP-0); discarding.
(WW) NVIDIA(0): Mode "1152x768" is too large for LG TV (DFP-0); discarding.
(WW) NVIDIA(0): Mode "1152x864" is too large for LG TV (DFP-0); discarding.
(WW) NVIDIA(0): Mode "1400x1050" is too large for LG TV (DFP-0); discarding.
(WW) NVIDIA(0): Mode "1440x900" is too large for LG TV (DFP-0); discarding.
(WW) NVIDIA(0): Mode "1600x1024" is too large for LG TV (DFP-0); discarding.
(WW) NVIDIA(0): Mode "960x600" is too large for LG TV (DFP-0); discarding.
(WW) NVIDIA(0): Mode "960x600" is too large for LG TV (DFP-0); discarding.
(WW) NVIDIA(0): Mode "1024x768" is too large for LG TV (DFP-0); discarding.
(WW) NVIDIA(0): Mode "1024x768" is too large for LG TV (DFP-0); discarding.
(WW) NVIDIA(0): Mode "1152x864" is too large for LG TV (DFP-0); discarding.
(WW) NVIDIA(0): Mode "1280x1024" is too large for LG TV (DFP-0); discarding.
(II) NVIDIA(0): Assigned Display Device: DFP-0
(II) NVIDIA(0): Validated modes:
(II) NVIDIA(0): "1920x1080"
(II) NVIDIA(0): Virtual screen size determined to be 1920 x 1080
(++) NVIDIA(0): DPI set to (100, 100); computed from -dpi X commandline option
(--) Depth 24 pixmap format is 32 bpp

You can change the gui x and y size and offset somewhere in the mythtv settings. If you are happy with a bit of overscan on your videos, it is best to pick a video mode with a bit of overscan (as your comments suggest that you have done) and then adjust the aforementioned parameters so that the mythtv menus fit the screen perfectly. This will prevent the menu text from being cut off.

Your suggestion worked great! Thanks.