I bet in HL3 he will start to hand it to you, but then the place will be attacked and you'll be forced out of it by G-Man (who then will freeze time and ninja it.)
Blow up the gunships, then look and you will see where the portal is comming from and launch the energy balls at that. It revolves counter-clockwise I beleive.
After the second one, use your minipulator and bring one of the turrets with you, it will come handy in the last part.
I set up two facing one way with boxes around them so they could not be knocked over, and me and another turret on the other stairwell, use your minipulator to get the...
There are combine on Earth, Mossman when you first see her says something like "Once combine come to Earth, they are stuck here." Or something like that, but, most combine are part of the Overwatch.
On one of the security camera places you get to see a combine medical lab. One of them has no clothes on with the exeption of his pants. He looks creepy.
Fast Zombies and Poison Headcrabs
I hated the combine for a while, then the last part where your gravity gun gets steriods kind of made me pitty them ;)