constepatdyak :
He doesnt need 64bit...he only has 3g ram so 32bit is fine
Please stop spreading misinformation. 64-bit apps (if you can get them) can have speed benefits (think image/video processing, encryption). Even 20% depending on application.
Just because 4GB=2^32, it does not mean the CPU does not allow any access above. 32-bit Server versions of Windows allow using up to 64GB RAM (36-bits), with any CPU starting with Pentium Pro (1995 I believe). Because of fear of cheap drivers (PCI devices are still limited to 32-bits, so special handling is needed for 4+GB DMA operations), MS chose to artificially limit the desktop versions to 4GB. Using the DEP/NX-bit already has the CPU in the mode that allows 64GB RAM.
In short: if you use 32-bit apps, there will be no speed difference, but if you can get 64-bit apps, then 64-bit platform will be faster. Also, no matter what OS you are using, 32-bit individual apps will still be limited to 2/3GB (so using 32-bit apps in 64-bit windows on more than 4GB is beneficial when many RAM hungry apps are running simultaneously...i.e.: not for gaming).
So my comment is related to reccomendations of 32-bit only. The Home Premium/Pro/Ultimate comments are ok by me.
PS: the OP never mentioned the intended use, so I cannot deny the 64-bit platform (which currently is useless for gaming).