I have spent about 5 hours trying to get zombie panic source to work. I have a LEGIT version of Half Life 2 (Required to make it work) and Steam says its installed but i need to install SDK 2006 (I think its called) to let the game run. But steam says "Steam is busy right now, Try again later" (Or something like that) Please help me, i cant do anything else because i cant think of anything else.