If the executable files (winword.exe, excel.exe, outlook.exe, etc.) are located in "%SystemDrive%\Program Files", you have the 64-bits version.
If they are located in "%SystemDrive%\Program Files (x86)", you are dealing with the 32-bits one.
Cheers.
[Edit]
Indeed, if standard installation path is changed, this method won't work.
According to
SO: How to programmatically detect 32-bit or 64-bit visio version is installed?[
^], you have some more options:
- you can check in the registry whether corresponding keys exist in
HKLM\Software\Microsoft\Office (64-bits) or
HKLM\Software\Wow6432Node\Microsoft\Office (32-bits)
- you can use the
GetBinaryType function[
^]
[/Edit]