At this time, you cannot mod portal. You will have to sit tight for the SDK to be updated.
Hate to break it to ya, but I highly doubt they will ever release the source code for Portal. CS/DoD source code has never been leaked so I highly doubt Portal ever will.
Well considering we have already gotten the Episode 2 SDK update...I highly doubt anything more is coming. I am assuming he meant the configurations for creating Portal maps and stuff, not the actual source code for it.
Hammer has been updated for the Episode 2 updates, but the full Orange Box updates to the SDK Base have not been released.
I dunno, I just have a gut feeling that they Portal source won't be released for a long time, if ever. They only have one or two guys that work on the Source SDK so seeing that major of a release is not foreseeable for me.
One day! One day who knows?
Someday! Someday I suppose.
You can do that for anything...it doesn't really accomplish anything except add unnecessary icons in the Steam games listing...
i think making it a mod is a better idea, no other custom maps to clutter up the bonus list, a campaign list, new scenes, etc.