On boot camp, 64-bit is only supported (somewhat) for Vista. Same goes for MBP. Office 2007 is a program, its coded in 32bit, not 64. Doesn't matter since 64bit OS can run 32bit programs, just not 32bit drivers.
32bit vs 64bit is memory usable mostly. If you have 4+ gb, 64bit is better, less then 4gb ram, 32bit is easier. Its personal preference.