afaik CS 2 will run on the hl3 engine.
You mean the Source engine? I'd be surprised if Valve pull away from that engine anytime soon really. It's a good system, just cumulatively update that same engine instead of having to start from scratch every time. It also has the added benefit of the older games running on the engine benefiting from the new updates (i.e. the massive HL2 upgrade that happened last year).
nah, there's no way CS 2 will follow the source engine. they will bring it out when they bring out HL3 for sure
I'm not too sure - CS2 is coming out pretty soon (or is intended to come out soon anyway :/)
Also do remember that it's not actually Half Life 3 we're waiting for, it's Half Life
2 Episode 3

Do remember that Valve designed the Source engine so that they can just keep continually updating it. In my opinion, it's by no means out of date (it looked pretty damn good in Portal 2).
Either way, if it turns out that I'm right or if it turns out that you're right, it'd be a new Half Life game. I don't care what engine it runs on. (I'm not overly fussed about the new counter strike.)