I suspect it might be some other software loaded that is causing the problem.
Make sure everything is shut down; firewalls, anti-virus programs, anything and try it.
It could also be some installed application that has some DLL loaded causing the problem.
It's not video card driver related as I am running the same driver in 2 diferent computers (Windows 2K Pro) without any alt-tab troubles and I usually have a gob of other stuff in back ground.
It might be DX9, as I am using DX8.1b.