Half Life 2: Final Preload
Looks like Valve has initiated phase 5 of Half Life 2 preload on the steam website. Of course, you can’t play it until it has been activated. Plus you can’t activate it until Half Life 2 boxes hit retail. Plus Half Life 2 won’t hit retail stores until the legal battles between Valve and Vivendi Universal Games have settled (kind of).
The moral of the story is that irrespective to all the hype about Half Life 2 preload, steam users won’t be playing the game any time earlier than ordinary buyers.