you cannot go wrong with an amd 64 bit processor right now.
intel really need to get their act together, as amd is quite simply leading the market in terms of performance and price.
You wont lose anything by running a 64 bit processor with 32 bit OS/software as amd kindly added support for 32bit applications. they run perfectly.
the only problems you may have is running 32 bit apps on a 64bit OS, but til microsoft iron out all the bugs in X64, and the companies get patches and drivers out of BETA, you dont need to worry about it.
amd 64, all the way.