Oh right. Skimmed through your first post, sorry. Hmmm. Not real sure here. Most people will tell you the usual: Shut down unnecessary tasks, don't run any background antivirus programs if you don't need to.
did you update to 5.7 catalyst drivers? My 9800 runs smooth with them. I was also able to get stable gameplay with midrange FPS out of Doom3 when I had the Mobility 9700 in my XPS, medium settings of course, so I can't believe your 9600 won't play freaking CS:Source.
Somethings bloating the system. Try either reinstalling the current driver or go to the new Catalysts. Here's a link from DriverHeaven for the mobility Catalysts:
Defrag.
Add/Remove unused programs.
Check
msconfig by using Windows "run" app. to make sure you've unchecked all programs from the :C drive you don't want starting up with Windows
Download Cacheman, and run a memory optimization to ensure as much of the game is running in memory as possible.
These are mostly tweaks, but you check that you've downloaded the most recent DirectX support to date. Steam has reminded me before, but that was on nVidia supported cards. I've never been scolded by Steam to update the ATI card.