Hi John,
Actually, there is no mismatch in having 32-bit Office installed on 64-bit Windows. In fact, this is probably the preferred environment. SAPGUI in general is much happier with 32-bit Office, especially older patches (by the way, 7.20 is no longer in support -- you should upgrade to 7.30).
The errors you're receiving are most probably related to lingering 64-bit components of Office on your workstation. We had the same situation in my office a while back, when we first started rolling out 64-bit Windows to a few users, and the PC techs mistakenly thought that meant they had to install 64-bit Office. That caused lots of problems, since 64-bit Office is incompatible with many things, not just SAPGUI, as you found. Correcting the error by simply reinstalling Office 32-bit resulting in workstations with some 64-bit and some 32-bit components, and that just made things worse. Systems where 32-bit Office was installed from the beginning (on 64-bit OS) had no problems at all.
So, what you're probably going to need to do is to uninstall all Office components (including Outlook, Visio, anything like that, not just Word and Excel), and also uninstall your SAPGUI, then reinstall 32-bit Office (with Outlook) from scratch, then reinstall your SAPGUI. This will probably clear up your problem.
Regards,
Matt