Gabe Newell (founder of Valve) posted this note on Voodoo Extreme, chock full of info on CS:CZ and beyond:
Counter-Strike Condition Zero is a collection of single-player missions...It's being built by Erik Johnson's team, Minh is in the loop.There's also some interesting news on TF2, so take a look. This is about as official a confirmation of CS2 as we've seen.
What's Minh working on? He's working on Counter-Strike 2, which will use the same engine as TF 2.