In dire need of help! NEED MY DOSE OF GAMING!

I've been experiencing some drastic graphical problems with a few games I've tried running on my PC.
My PC's rather old (Pentium 3 1000), but my graphic card is a pretty new (bought less than half a year ago) Geforce 7600.
Thing is some games run smoothly enough without any problems (except the usual glitches of course ).
The games I've experienced the problems with: Vampire: Bloodlines, Prince of Persia: The two thrones and Psychonauts.
In all of these games the graphics are EXTREMELY glitchy.
I'm talking wireframe like characters (as in full of holes and such), and same effect more-or-less with background. I've also seen the problem occur with the 3d text windows screen saver.
My guess is the newer games use a certain technology which older games do not use. I'm pretty sure the problem has something to do with the Direct3d.

check these out if you want to understand what I'm talking about glitches:

http://www.yourfilehost.com/media. [...] =PNss1.JPG

http://www.yourfilehost.com/media. [...] =PNss2.JPG

http://www.yourfilehost.com/media. [...] dtxtss.JPG

I of course, did the usual:

1. I have the most recent directX.

2. Updated graphic card drivers.

3. Ran dxdiag - checked out FINE in ALL areas.

Kinda stumped now....My last thought is updating my Motherboard BIOS, which is pretty old hardware and so MIGHT be incompatible with the graphic card. But I don't really want to mess with the motherboard BIOS till I'm sure it's the right thing to do.

Anyone have any ideas here?

Why are u even trying to game on a P3?