Windows XP only see 3gig of ram
Yes your computer may support up to 8gig only Xp or vista or windows 7 64bit will see and use ram above 3gigs
If you have two gig ,one more will not help that much in games,, but it will help a bit.. at that price I would get them anyway, Until you can get a better video card. Your main handicap is the video card has only 265mb,,, vcard with 512mb is pretty much a must now.
decent cheap cards
68$
http://www.newegg.com/Product/Product.aspx?Item=N82E16814161252
http://www.newegg.com/Product/Product.aspx?Item=N82E16814131146
http://www.newegg.com/Product/Product.aspx?Item=N82E16814121314
79+$
http://www.newegg.com/Product/Product.aspx?Item=N82E16814102822
http://www.newegg.com/Product/Product.aspx?Item=N82E16814127418
Hope it help
Syn