Personally I would stay away from the ATI line of AIW cards, their support for this particular line is poor at best, they don't spend the time on them they need too, and their WDM drivers are a source of constant problems, everything from from stopping capture of any source to just plain not working, or video/audio sync, long pauses between channel chnages, they also introduce a Macrovision guard module, if it's detected it will present problems. I got so tired of the WDM problems and not having the ability to record from my very own VHS tapes, that I removed every single one of them from my systems, I won't use the AIW cards again, they just aren't supported properly. As far as AGP and or USB only, you limit yourself considerbly, but their are items that will fit the bill, just not at $50.00
you do have a couple of choices:
In one of my systems I use the personal cinema 5700 256, I've not had many problems with it, but I find it better supported.