If I'm running a 64-bit OS (Windows XP x64 edition) and a program has both a 32-bit version and a 64-bit version, what are the advantages of using the 64-bit version? Will it be faster?
XP 64-bits is not more secure than 32-bits.
Vista and (better) Windows 7 introduced in 64-bit mode enhanced security with hardware-backed DEP, Kernel Patch Protection and mandatory driver signing.
So the only advantage in XP is that a 64-bits program can use more than 4 GB of memory.
if you run the 64-bit version, it will be able to address more memory, and if it is optimised well (as are some games) there may be a <10% improvement in performance. But in general it is not felt by the endusers.
i think most people run 64-bit just because of the memory addresing concerns.