Re: LeadTek 6800 128mb Low performance
The OS showing AGP 2x is normal, as long as it says 8x everywhere else.
Have you checked to see if vertical sync is disabled, both in the driver control panel and the game? Also, 768 MB of RAM is a bit low. HL2 runs better on 1 GB and ideally on 2 GB.
The power supply also could be an issue if it's generic. What is the +12v rating? You'll need to open up your case to find out.