First of all, the demo contains two missions that are NOT included in the full version - it's a kinda prequel to the game, so it's worth downloading. As for the gam, it's been some time since it was released, but there still are copies to buy - I've seen some on ebay (some time ago), you could also try other online shops. Another option is searching a second-hand copy. Anyway, I think you'll receive more info from TLR members soon.

I don't have a drinking problem. I drink. I get drunk. I fall down. No problem.
(stolen from a local pub)