According to a company spokesperson from Valve Software, the full version of Steam will be available beginning next week. Valve founder Gabe Newell calls Steam "a broadband business platform" and "high-performance distributed file system for fast, scalable content delivery."
A Valve-circulated document states, "The Steam Beta has delivered several Valve games and popular Half-Life mods to over 300,000 gamers and will come to a close [next] Tuesday evening. The first full version of Steam, Valve's broadband platform for the delivery and management of digital content, will launch...on Wednesday."
The steam site has additional information.