Though I wouldn't want to pay for XP64 bit then pay again for Vista64 bit, but you can get Vue6 now and then upgrade to Vista 64 bit when it comes out.

I have had confirmed from e-on that you effectively get both a 32bit and 64bit version of Vue6 (at least for Infinite) for your money and the 'correct' version will automatically be installed (so if you install Vue6I on WinXp it will be a 32 bit version, if you install on XP64 or Vista64 it will be the 64 bit version) so all you need to do is re-install Vue6I once you have upgraded to a 64 bit OS.