Well, what is hopefully not far off the last Half-Life2 preload has begun, check out steampowered for full details.

The seventh phase of the Half-Life 2 preload begins to Steam account holders today. This will allow users to download localized Half-Life 2 content and other content in encrypted form. No purchase is required to pre-load Half-Life 2, but is required to activate the game. The moment the game is made available, those who have pre-loaded and purchased the game via Steam will be ready to start playing.

CS-Nation also have news of when you'll be able to unlock all this preload content and get playing! For us Brits that would seem to be 8:00AM (Nov 16th). Click here for the release information.

It would seem that at least part of the SDK is available now also.