Valve has announced that those who pre-purchase the Orange Box over Steam will get the Team Fortress 2 beta next week, on September 17.
The price is 10% lower if you pre-order it on the Steam, so the Orange box will cost $49.95. If you don't like the price, here is another info for you. Listing in the Steam online store indicates that if bought individually, Orange box games will cost around $80 in total.
The PC and Xbox 360 versions should hit Europe on October 12th and the US should see it a bit sooner, October 9th. The colored box will contain Half-Life 2, Episode One, Episode Two, Portal and Team Fortress 2.