You would know if you were overclocking.  You would either have an applet
provided by the motherboard maker that allows you to adjust voltages to
increase the cpu or memory speed or you would knowingly make such changes in
the BIOS.  Not that all overclocking is bad, sometimes it is useful to
finetune various combinations of hardware, but overclocking to push
performance of a game can be risky because gamers keep trying to squeak out
just a little bit more, etc.

I would take this issue to the microsoft.public.windows.vista.games ng as
well as here to see if others playing some of these games have run into the
problem and have a lead for you and I would use any forums on the game
maker's websites for help as well.

I still suspect the audio and video drivers for your system.  If you bought
the computer with Vista preinstalled then I would try to stick to the
manufacturer's website for the drivers.  The more generic ones for your
adaptors may not be right.