Well i'm not sure it's even got anything to do with the disc, mine doesn't even check the dvd or spin it or owt.

I can't see it being an issue with my cd drive, as none of my other games seem to have a problem in finding where it is to run games.
although it could be that i have a different problem to you guys, i dunno. i mean, i guess the problem is that steam has no real way of dealing with, or telling you what problems are, chances are, we could all be having completely different probs, and steam isn't doing anything to tell us!
i've looked everywhere, in the windows error reports, the steam report file, hardware problems and conflicts, everything i can think of.
obviously, valve haven't emailed me back in the 24-48 hours they promised, but i think that's mainly due to their system being clogged up by the whiny *****s who emailed them because they couldn't get their copy to work within half an hour of it's release. (man, do those *****s annoy me, i've been going for over a week, now THAT's annoying.)
but it's good to see that more people are coming into this thread, although it gets more and more perplexing as none of us seem to have any one particular hardware trait that could be seen to be the problem... hmmm..