New install of office, COM calls fail for version reasons?

We recently replaced an ailing machine with a newer one, which cured
most of our problems. However, the new office install, 2003 SP3,
appears to have COM version problems. I say this because there's a
piece of code that calls MailEnvelope in Excel, which is now failing
but worked fine on the previous machine.

Looking around on the 'net, most people agree that the problem is due
to versioning, typically having the wrong version of Outlook or Excel.
However, all the versions are identical when I look in About... and
are definitely versions that support this function. This leads me to
believe the call _should_ work, so the problem may be a little
deeper... corrupted registry perhaps?

Can anyone offer any advice here? A re-install is doable, but I'm not
convinced the problem won't still be there.

Maury