Either would work, but you would be running in single channel mode. Run your memory modules in matching pairs to take advantage of the dual memory controllers. The Corsair XMS 4GB (2x2GB) kit below is $18 after rebate. http://www.newegg.com/Product/Product.aspx?Item=N82E16820145251
Or if you don't want to deal with a rebate.. GSkill 4GB (2x2GB) for $21...http://www.newegg.com/Product/Product.aspx?Item=N82E16820231396
Having a 32bit OS will hinder you a bit by only using 3.5~GB, but you stay in dual channel mode.