with HL2, you pay for one 'licence key' and then can play your 'copy' of HL2 on any PC, still only paying the upfront cost. Using this method means for things like TF2 etc you will have to pay a fee (if they are released as exclusive content and not a free-MOD that is...) The other option is a monthly fee which gets you
anything valve releases over steam.
In regards to getting CS 1.6 going,
www.ausgamers.com have a version of steam with it included in the cache (not sure if other file places have it [edit: didnt see post above regarding this] ) but thats what i used to get going. I am on dial up in australia... and i can play on US servers almost normally in 1.6 (no idea why).