IF it's coming to X-box -- no word yet. Although I must admit, I'd be seriously hacked off it was an X-box exclusive, even though I have one.I dunno. This is just wild speculation, but I suspect the engine will be at least on par with the Doom III engine, and I don't think any other console could really pull off Doom III. So if that's the case it'd make sense for HL2 to be Xbox exclusive as well.
The biggest surprise they could pull off at E3 would be Metal Gear Solid 3 on GameCube without RaidenMGS3 is another game I'm waiting for. I'm just hoping that that NGC exclusive contract was for the MGS1 remake and not MGS3.
So many sequels, so little cash for a PC upgrade.