Sounds like your video card driver came with an applet that has quick keys / macro's defined to do this. Both ATI and NVIDIA based cards ship with a utility that runs in the background. These applications are not needed for drivers to work. Look by the clock there will be a red and white diamond shaped thing for ATI or a green squiggly thing for NVIDIA. Try right clicking and see if you can disable it there.
If not you can always stop the application from starting with Windows via the registry.
Here's how you stop it in the registry (example is the structure in XP since its the most common OS)
Start --> Run --> Regedit
Expand the tree as follows
HKEY_LOCAL_MACHINE
SOFTWARE
WINDOWS
CURRENT VERSION
RUN
Locate the key for your NVIDIA or ATI panel application and delete it. Restart your PC and its gone. Video drivers will still work, but quick keys, etc wont.