the thing which pushed me to use the x64 compiler was the 3GB limit the 32bits programs have when allocating memory on host memory. Performance-wise you'll probably have no noticeable difference on running kernels for x86 or x64 (unless you hard code some optimizations).
Otherwise, if u'r from an university you can maybe have a nice price for the pro version (can be up to 10x less than the usual public price, if not just free!). else, you can try using GCC for windows and/or check out Eclipse (.org) too (open dev. platform), although i've never tried using (you won't have the AMD profiler plug-in(?), but well, that's a little price to pay for not paying the 1k$ MS VS pro!). last case, go for linux and use gcc!
