After installing Steam, it demanded an update of 127 MB. But I don't have an Internet connection. So can I download a pre-updated Steam from any other computer which has an Internet connection?
It seems like you can do it by copying the whole Steam repository from another computer where steam is fully installed as @aytimothy said and as it is explained here : http://steamcommunity.com/discussions/forum/1/828934913076877521/
If you copy it from a friend or so, copy everything except the SteamApps repository because it contains the games.
But steam is constantly updated and is really thought to be used with an internet connection.