Well, I'm happy to tell you that you're wrong there! You can play CS, quite well actually, in Linux. You can play it in WINE(free), or to do it perfectly, you'll need Cedega (WineX 4.0). Cedega requires a $15, one-time subscription to TransGaming. Well worth it if you ask me. Check out their compatibility list!

-AT

P.S - Please forgive the horrible-looking WindowMaker desktop pictured below; I'm not running HL/CS, so I had to "borrow" the screenshot.