Different than my problem, I was only freezing for a quarter second or so (but as i do music, that's enough to make the computer useless.)

Your problem sounds like not enough memory in your video card / and or not a fast enough AGP bus speed of your video card... so your game is "texture thrashing" - runs out of texture memory on the card and has to swap it out to Windows memory. Just a guess.

I'm getting a similar problem playing Half-Life 2 on this machine (with a 4X NVidia GFTi4600 128 MB ) - plays great for 20 minutes or so, then freezes up (while audio gets stuck in an annoying loop) for entire minutes at a time... then it gets better again for a while. And so on.... Time to get a new 8X card i think!

FYI