Context Menu Appears without right click

A colleague of mine has a very new Sony Vaio laptop with Vista Business
loaded. Plenty of memory. She is experiencing a bizarre problem where the
context menu (usually but apparently not always the one that would appear if
you right click on the desktop) keeps appearing without her right clicking.
It happens so often that the computer is essentially nonfunctional.

We assumed it might be a defective mouse but that was readily disproved by
switching mice. Does anyone think this is a hardware problem, e.g. some
problem with the the touchpad, or is there some software setting problem? Or
do we just have some corrupted driver or other software?

Thanks for your help.

Michael Karlin