I agree as well. My experience with hardware is limited mostly to installing hard drives and RAM, but having read many articles and forum posts on this issue, a 512MB video card is the minimum recommendation for serious gaming. A 1GB one would be preferable, as long as the computer will run it, and your budget allows for it.
As far as eBay buying goes, Nibiru gave some excellent recommendations, you have to research what you're looking for, have some kind of idea of the going market prices in your area, and don't rush things. Know what you're bidding on, the terms and conditions of the sale, such as the seller's return policy, many charges a "restocking fee", some allows no returns for "buyer's remorse", but defective products only.
eBay can be a really good source of computer parts, I've scored a few really good deals myself. But you must have patience, and do your homework well. There has been some solid advice given as to how to make purchases and being a good bidder. There are also some tips on the site, too.
Cat