If you have more than 3GB of RAM then you should go with 64-bit. But either will work.
Now just because it works doesn't mean Apple supports it. On some computers Apple has not been including 32-bit Drivers in its (Boot Camp) Windows Support driver package. So keep that in mind.
If you're going to be use windows by way of vmware then I'd recommend using the 32bit. The potential benefit of 64bit computing is overshadowed by the overhead needed by vmware to handle the OS.