There is no native 64-bit version of Office 2007.
There are some very minor benefits. When you install Office 2007, the installer automatically checks to see if you have a 64-bit OS and installs a few x64-specific files if it finds one.
I'm not entirely sure what those files do, but I would assume that the dlls control things like database access, etc.
So, yes, Office 2007 is slightly x64 enhanced, but probably not in any way that you would actually notice.