I have no knowledge about HL2 and CS:S. I don't have the game, too. I even don't know if I'll have time in the future to learn that stuff and work on it. I guess we will need someone to port it to CS:S and continue it in CS:S.
Source engine is completely different - and rather no bot can be converted to Source games lik Counter-Strike:Source without writing the code from scratch
Well, i read the hl2sdk this days, and yep, it's a bit (maybe more ) differ from old one (hl1sdk), but if valve even provide good additional interfaces for their server plugins, maybe it will be possible to port podbot to source. They promise somthing year ago, but still no any news