'Official' Half-Life 2 Thread. Do Not Create New Threads (NO SPOILERS)

[GLH]

Originally Posted by GLH

Can anyone tell me which files i have to store on a DVD+R, so i don't have to redownload it, when my PC crashs?

So now i found out, there is a "Backup files" option in the Steam-Menu (right-click on the game title).
But when i do that, Steam tells me "Half-Life 2 kann erst gesichert werden, wenn die Aktualisierung abgeschlossen wurde."
(english: Half-Life 2 cannot be backed up until it has finished updating.)

Which actualization/update?
When will it be ready?
I can play the game without problems!
How can i tell Steam "update now"?

PS: It's a very cool game!