I've installed Half-Life from the CD-ROM but Steam was not installed. Even after the install is complete, I can not play the game. Is Steam required for the older games like Half-Life?
The installation from the game disc for all Valve games prior to Half-Life 2 will no longer work. These games need to be downloaded and installed through Steam.
Please follow the Activating a Product on Steam guide for instructions on how to register your game on Steam and download the game content.
Do not discard your game discs, the game's packaging or your CD Key as this information may be necessary for proof of purchase at a later date. Store your CD Key in a safe place.