Vista - Problem in Gaming

I have a problem that really bothers me.
It is a game problem, when i'm playing a game,
after like 3 minutes it starts to bug, like if the framerate was really low.
The game i'm playing is LineAge II ( Good Graphics though ) and it is online.
I don't think it is a network problem, because if it was it wouldn't
run smoothly the first 3 minutes. I'm running x64 Architecture.

Edit: If i shut the game down, and wait for like 1 minute and play again the problem goes away and i have 3 minutes to play ( Lol )

Hopefully your 8600M has a temp sensor on it. Grab this,

GPU-Z Video card GPU Information Utility

run it and click on the Sensor tab, if there is a temp sensor it should report it. If so put a check in "Log to file", then run your game. Once it starts slowing down check the log and post back what the highest temp was; also what it is/was before running the game (idle).

If it is what I think it is that is happeneing, the only way to fix it will be to contact Asus about an RMA. In case you don't know what I am referring too,

http://www.techcrunchit.com/2008/07/...efective-gpus/

and yours is one of those.

Damn it, i think you're right.
Now, without playing anything its 98C.
I'm going to have to send my notebook to asus again. =(