If I buy a game that is a disk, will it work on multiple computers though Steam?

I am getting a gaming computer tomorrow and I am getting Battlefield 3 and Crysis 2, I don't know much about PC gaming so I want to know, can I install a game and make Steam know that I have installed it? Even though I didn't install it though Steam? And can I have my stats on both of my computers if I use the same Steam account with the game?If I buy a game that is a disk, will it work on multiple computers though Steam?
You can make 1 steam account and use it on multiple computer just bring up steam and log in.

You can add it as a "non-steam game" so you get the Steam overlay with friends, chat, etc., but you can't register it as a Steam game, sadly only if you buy it from steam so you will not be able to get updates and things for your game unless you buy the game from steam but you can still add it as a non steam game.

https://support.steampowered.com/kb_arti鈥?/a>If I buy a game that is a disk, will it work on multiple computers though Steam?
yes