I use mythtv on an FX 5200 w/ svideo out on a 25" RCA TV. Using the nvidia-settings tool that ships with the linux drivers, I managed to get all the scanlines to match up, and I got a remarkably clear picture. The biggest problem is the lack of geometry controls to make everything straight again.
My biggest suggestion is moving to 720x480 for your resolution, and jiggling with the oversan.