Well... Now I have everything up and running. Including CS:S. the problem is that it loads for a while, then the background screen turns sideways, then is cut in half by a diagonal stripe of agony, then the menu appears, but all of the characters are terribly corrupted, bearing no resemblance to the words that they're supposed to.
I'm using a rather crappy graphics card (nvidia gforce4 MX I believe) so maybe that's the problem?
oh, yeah, and when I quit, it puts me back onto the desktop at 800x600 res, and the buttons of steam (minimize, close, launch, etc.) no longer work.