If you are talking about performance of software on the two systems, you should look through this article: http://www.extremetech.com/article2/0,2845,2280808,00.asp
Conclusion is that performance is a mixed bag, with 64 bit software not quite mature.
You do have to have 64bit hardware to run Vista64, but virtually all pc’s made in the last few years have that capability. More ram helps too, but Vista is a memory hog in either configuration.