In order to work in Norway, knowledge of basic Norwegian is required at the very least. As a member of the European Economic Area (EEA), Norway grants citizens of other EEA countries the right to look for work for a three-month period without obtaining a permit; those who find work have the right to remain in Norway for the duration of their employment. For other foreigners, it's very difficult and an application for a work permit must be made through the Norwegian embassy or consulate in your home country before entering Norway.
In Oslo, Use-It is a useful resource.
For help with looking for work, the best place to start is the Norwegian Labour & Welfare Organisation, which produces extensive online information for free.