With the latest set of drivers (and the one before that I think..), I'm experiencing a weird distortion when viewing movies fullscreen when using the tv-out. Fullscreen on the pc looks great, and anything but fullscreen movies (tested with wmp and windvd) looks great on tv.
Switching to full screen, makes the leftmost part of the picture, wrap a little bit.. but not all of it.. every five lines or so.. Hard to explain this
The end result, is that the picture looks a bit fuzzy. Earlier driver sets looks great, but with them I've experienced some texturing problems in a few games..
i may have had the same problem as you have. i am running a 4200 and at one point when i tried to video out at full screen it was messed on the left side and was sort of pixalted.
after awhile of looking around i saw that when i went into the clone mode that it was playing in 16bit color.
in order to change that make sure u have something hooked up to your tv out. and then check if its in 32bit color.
not sure if this is your problem but you can try it out.