unactivating a game..?

[yangsta]

A friend wants to give me his hl1 key but I can't use it because he already activated it in the past, but he doesn't use it at all. Is it possible to deactivate a game?

 

[Beerdude26]

Well, you can, but you have to send a wad of stuff (your actual CD key, your receipt, etc) to Valve, and include 10$ and then they'll let you transfer the CD-key to another Steam account.

 

[Barney Fife]

Or you can buy the actual new, never been used, HL1 and get it over with, HL1 doesn't cost that much, Heck, it costs much less than the whole wad of stuff Beerdude told ya.