If you want to get some preformance out of the game, just get a new motherboard. You can find a relatively cheap yet high preformance barod for about $90 or so that supports 4GB of PC3200 ram, and 8x AGP.

Also, getting DDR ram will help your preformance a bit more, btu I think you'll see more preformance upgrades with a faster Hard Drive and you should be set with that video card. Howerver I do not recomment buying from best buy. Sure they are a nice store but you won't always get the best deal there. I like http://www.newegg.com and http://www.tcwo.com
They have cheap prices and quality parts.

Also since you playingi BF:V, check out my website for a clan I started.
http://americanrebels.net