Anyone had any success using the Riva TNT card for mythtv? Here's what my problem is:

I can install knoppmyth using the composite tv hookup, but when it goes through the first reboot, it just comes up to a blank screen. I can hook up a vga connected monitor, and it works just fine, and I can finish the setup.

I've tried using quite a few different config files to get it going, including just copying the nvidia-tvout.sample, and I got errors such as no screen found and a couple others I can't recall (I'm at work, and my scratch papers are at home). I tried the nvtv packages, and all I got was some garbled junk on my screen. I just used the card because I had it in a pile of junk. Do I need to get a newer card, or will this one work? I've got a headache from banging my head against the wall. Thanks

Are you using the latest drivers? Don´t, since Nvidia dropped support for TNT/TNT2 and Geforce 256 series a few versions ago. Find some older drivers and try, look for more info on Nvidias driver pages.
The drivers bundled with XFree86/Xorg, should still work.