That should be fine. I have a 64M Radeon 9200 in my machine, but I'm using a PC monitor, but ATI is supposed to be good for S-Video.
One thing, you can't use later than the ATI Radeon 6.5 Drivers with that card, but otherwise, it sound fine. (And that's not a hardship, just don't download their 7.1 Drivers and wonder why you get a black screen.)