There are one of two ways doing it, You have to buy either half-life or couner-strike. If you buy half life you'll have to download the latest version of counterstrike for it, If you just buy COunterstrike like me, then you'll have to get the latest Patch. You cant just download it, it has a CD key, and even if y ou were to find one on the internet it would only allow you to play lan games or single player games. WON needs to verify your CD key and if its already in use, you wont get into any servers. Its only about 30 dollars and you can find it in almost ANY store that has a small computer section. But i would choose EB(Electronics Boutique).