go to esf-world.com download beta 1.1.
install it to c/programfiles/steam/steamapps/youremail/halflife
download the esf steam patch from the same place
install it to the same directory
your good to go
i would suggest downloading evm and eea also. put them in the same directory but make sure you still have the evm models because eea models suck. u really need to do this because there is only a couple of servers on steam, and if you dont have both evm and eea then you prob wont have access to many servers.
*edit*
if you dont have steam, search for the official counter strike homepage and download it there.