window分別問題

the main diffrence is if your CPU is 64 bit capble.
applications and windows will work much faster then 32 bit.

main problems is not all applications are 64bit capble.
dont get 64 bit on vista or XP you will have problem after problem to run drivers and software.

Windows XP 32 bit can address about 3.2G memory only. if you've 4G or more memory, the rest of the memory after 3.2G is wasted.

Windows XP 64 bit can address much much larger memory.