Okay, so it’s fairly obvious that you can only run 32-bit (x86) windows on a 32-bit processor, but of course a 64-bit processor would run both an x86 and an x64 OS. So how do you find out which “bit-version” you’re actually running? Easy. WinKey+R (to bring up the run box) and then type “msinfo32”.
The “System Type” line in the right-hand pane (when clicked on to “System Summary” on the left) will tell you the bit-version; so, for example, the VMWare PC I’m typing into now reports it’s an x64-based PC, but my other VM is an x86 Windows XP PC (and they’re both running on an x64 version of Vista Business with VMWare 7)
So, regardless of what your processor is capable of, you’re limited to whatever architecture of Windows you’re running; you can’t install 64-bit Office if your version of Windows is 32-bit, even if your processor can support x64 programs.