Positional tracking is working, but is relatively subtle in game. Ramped up everything to full quality, 4xAA and it looks great on my i5 2500k with GTX 660. The Virtual Reality option is now enabled in options and once turned on a new 'Activate Virtual Reality' main menu option is displayed in HL2. Then I set DK2 to extended mode and started HL2.
I installed SteamVR from the Tools section in Steam.
