If you're looking for the best value video card for your system, I'd recommend this :
http://www.newegg.com/Product/Product.aspx?Item=N82E16814131360 $45 after rebate and free shipping.
You're going to have a hard time finding a new CPU for that motherboard. Probably have to get one from e-Bay.
I wouldn't bother with the memory. 2 GB is enough for XP and faster memory won't make enough difference to notice.
