For OEM systems especially Dell I use Crucial it just simply works.
http://www.crucial.com/store/mpartsp...44AF91A5CA7304
32 Bit OS's have a 4 gig mathematical address space limit including system devices and add in cards. You will most likely see 3.2Gig available to windows, but windows also limits programs to 2gig max over 2gig in XP doesn't give a lot of improvement in overall system performance unless you are running out of ram causing virtual memory hard drive writes/reads.