Some questions about Steam

Spirit Bomb -

1. I never bought any post-HL2 physical release from Valve, so I'm not sure; I guess you can install it on as many machines as you want, but you'll have to tie all the installs to a single Steam account. I'm just guessing.

2. Online is not needed. I usually leave my Steam in offline mode and it works flawlessly. If you don't have a connection, it will automatically ask if you want to use it offline (you must have previously saved your login and password); if you want to use it offline even with a connection, just go to "Steam -> Go offline" (on the top bar).

3. You can reinstall the games in as many computers as you want; you can even install them in various computers simultaneously - some of my games are installed both in my main pc and in my laptop right now. The only restriction is, if both computers are using Steam online, it won't let you start a game in both of them at the same time (if you leave Steam offline, you can play the same game on various pcs with no problems). This is the main advantage Steam has over, let's say, Nintendo consoles: the games are tied to your account, not your console, so wherever you install Steam and login to your account you can install all your games.

Spirit Bomb - No problem, mate! About your question, you don't have to uninstall Steam to access your other account. You just need to login to it with your other name/password, as you would do with an e-mail account or something. The games from one account won't show on your second account's library, so, to not have to keep alternating accounts, it's better to buy all your games with the same account. But no need to uninstall/reinstall anything.