Most should work with 64 bit.
Although I'm not sure about compatibility of some of them with WinXP 64 Bit though.  There have been a few people with problems.

It's just that most of them are not optomised to take advantage of a 64 bit processor or even Dual processors.

64 bit comes in handy though if you do a lot of high precision number crunching.

Only your mind limits yourImagination. Let it free.