Yeah just turn down everything. However, loads of npcs will also impact your CPU. the CPU would have to calculate the intelligence for all of the npcs. In games like UT2K4 - cpu generated bot intelligence can lower fps more than your gpu does. (Same deal with hl2) So not only do you need to turn down video settings to display them all, but definitely make sure that your cpu and ram are freed up when you run hl2, and nothing is running in the background.