Graphics card should automatically enable when you're doing something graphically intensive. If you want to force your machine to always run from the internal or dedicated graphics card, you can download GFXStatus and have control of manual switching. You can also leave it on automatic and you'll be notified when the graphic card changes, so you can see what sort of apps/games set it off.
It should be able to run Counterstrike, though of course if it struggles on higher settings (as it is quite an old card), just put them down a little to ensure smooth performance.