Horizontal scrolling not working in Office 2003

Using an MS Wireless Intellimouse Explorer 2.0 and the latest Vista 6.1
driver, horizontal scrolling would not work in Office 2003 after intial Vista
setup.

Mysteriously, a week later it suddenly worked, and very nicely at that. It
may have been related to a run of Registry Mechanic shortly before, but don't
really know.

After 7 MS Office automatic updates on the 15th of this month, horizontal
scrolling no longer works in Office. It does work in a few places elsewhere -
- like in the mouse driver settings dialog boxes. :-)

Any help? My reflexes are really getting confused!

For what it's worth, I found a simple cure that may or may not last: I just
unplugged the USB mouse and plugged it back in again. Don't know if this will
survive restarts etc, however.