Was away over the weekend, but it looks like jrnyhead gave some solid advice I would agree with.
The "numbers" on the cards refer solely to the graphics card. The video portion is unrelated, and is the same on all ATI AIW RADEON class cards. The 9000 series cards uses the next-gen THEATRE 200 video chips, though not much different from the THREATRE 100 (aka RAGE THEATRE) chips from the 7000-8000s series.
Used cards are often fine for about $50-75 on eBay
, but for a new card, the 9600 is the one to get, should be somewhere between $100-200, depending on where it's from (I've not tracked prices on those lately).
You should find most of what you'll need to know, in regard to capturing with ATI MMC, on digitalFAQ.com. The AVI and MPEG capture guides are on the main menu of this site, and it would be a good idea to read some of the other capturing guides if you have not already.
And then if you have any more questions, you're in the right place to ask.