Took me 3 hours from putting in the HL2 install disc to finally getting the game running last night.

Would have been much faster except that all of the official forums were down last night, and the faqs online absolutely sucked.
Turns out you can't have Steam installed BEFORE you try to install HL2. That was my problem, but there was no way of knowing that beforehand.
I also REALLY dislike the needed internet connection everytime you want to play. Don't expect to go to a LAN party and play this game. I do like Steam though.