8600gt problem plz help

hey guys.i bought a 8600gt a few days back and ran half life 2 on it at 1024*768 at the games own recommended settings but the framerates are choppy dropped the res to 800*600 still the same problem.so i ran the F.E.A.R in game preintalled benchmark at the recommended settings its like a slide show and samething happens even if i drop the res to 800*600 and dropped some settings and at 1024*768 it says it had a max fps of 130 and averrage of 48 which is not really visible duing gameplay due to excessive stutters. am on
2.6ghz p4
512mb ram
and 300watts max power power supply
plz help.i in my own opinion think that the psu is at fault because when i ran cod 2 it had the same thing and i reduced the texture from high to medium and it works well and about 1 hour into the game the system just shuts down.thanx

Your problem is almost definitely memory related. Load the Task Manager (CTRL+ALT+DEL) before you go into the game, then when it gets choppy come out. Have a look at the memory usage history graph.

If the memory being used while in the game is over your 512MB then the OS is using swap, and the game will run badly while it is. The solution is to get some more RAM so you have at least 1GB.

I have a 8600GT myself. Get 1GB more ram. Also 300w is the absolute minimum for the psu. Mine is 305w but I have 22amps. 18-20amps I think would be the safe minimum on the 12v.
Also I noticed in the 162.18 driver release notes that systems with 1.5GB of ram or less will suffer a decrease in performance (32bit XP). I use 162.22 (32bit Vista) and my system available graphics memory is 1535mb.