You should also think what version of OS it is. If it is Win7, then you should choose 64-bit to get the fully performance from your RAM. 32-bit does only support 3.2 GB. If you're choosing XP, then I recommend the 32-bit, due that the 64-bit is for developing purpose only, and therefor instable.
Also, 64-bit also takes double amount of space. If you have 2GB RAM and a 32-bit system, and then upgrade it to 64-bit, you need the double RAM to have the same percentage free RAM like the 32-bit.
Furthermore, even if this is only a computerspec, shouldn't you also think on stuffs like monitor(s), speakers, mouse and keyboard?
