Dungeon Siege II Issue

[dayvancowboy33]

Not sure if this is the right place for tech support buuut..

I start the game up, graphics are set to high, and the game runs smooth as butter. About 5 minutes go by and then I hit a massive lag spike, my frame-rate drops from 40 to 10. This lasts for about another 5 minutes then... its back to being smooth again? It will keep doing this switch back and forth constantly. The game only uses about 400mb of ram, and even when its being laggy, lowering the graphics to bare-bones doesn't make the slightest difference.

I tried setting the core affinity to 1, 2 or both, that doesn't seem to make anything better. I tried raising the app priority, but vista keeps reseting it i think. And oddly, by minimizing the game and waiting about 30seconds, the game will go back to being smooth again.
What is going on??

Specs:
Vista Home Premium
NVIDIA GeForce 8600M GT
Intel Core 2 Duo CPU T7500 @ 2.20GHz (2 CPUs), ~2.2GHz
2046MB RAM