DO I HAVE TOO?

Steam says my cd key is already being used......Do i really have to go and buy a whole new HALF-Life just to play esf?

Yes, you are obviously using a pirated version of Half-Life. I just want to let you know that if you had asked for a CD Key, you would have violated the Forum AUP, http://forum.esforces.com/announcement.php?f=2

To prevent this... I shall close the thread.

Well if you do own your own CD key and it says it's already in use you have to go to the steam website to get it worked out. You'll mostlikely have to have proof of purchase such as the cd cover with your cd key on it which you'd have to mail in.