System crashes on non-admin account

I run Vista Ultimate 64 on my "gaming" PC. Recently, I made a new
(non-admin) account to use day-to-day. When I play games (notably, World of
Warcraft, Age of Conan), I occasionally get system freezes. These freezes
are unrecoverable and require a hard reboot. Often I can tell when it's
about to occur because the mouse cursor has a graphics glitch. The mouse
cursor glitch is always followed by the system freeze. Typically, when the
system freezes, the colors of the pixels on the last image on the screen are
different than normal.

These freezes are extremely frustrating! I have noticed, oddly, that they
seldom, if ever, occur when I use the administrator account instead of the
user account. My system specs are as follows:

Vista Ultimate x64
Intel Core 2 Extreme QX9770
4GB DDR3 1333
Nvidia 9800GX2
EVGA nForce 790i motherboard

The Nvidia drivers are up to date. Can anyone offer me suggestions/comments?