It is not possible to have multiple users running steam (Windows 7). Worse than that, because any user can run steam, passwords are remembered between sessions. AKA my girlfriend receives my steam chat when she’s using my box.
The Steam client is not a system-wide service. It’s a game manager, chat client and browser (!?). Each user has its own steam account — it makes no sense to have these settings system-wide. What kind of design is this? Please fix it! (I’m aware this isn’t an open source project and I don’t really have anything to say about it, but it’s not a feature request. This is a flaw that needs to be fixed).