Hey all,
I was having the same issues with an MSI K8N (Neo 2 Platinum) and a 320gb Seagate SATA.
The first problem I was having was that my one and only SATA drive was showing up as /dev/sdb instead of /dev/sda.
After fiddling with BIOS and cable connetions and not seeing why it wasn't showing up as sda, I read that USB devices can sometimes bump a SATA drive from sda to sdb. Lo and behold but after disconneting all the USB peripherals except my wireless keyboard, the drive finally started to show up as /dev/sda!
Secondly, because my motherboard uses an nVidia chipset (nForce 3), I tried the steps outlined by nybbler in this
useful SATA initd thread
This got me up and running for the first time! Now I am off to configure Myth. Good luck to everyone attempting SATA! I hope that the SATA issues get worked out for future releases of KM, because it really is a fantastic project.