Currently under construction!
But here are a few links to get you started:
How to trace your ancestors in Norway, article.
The Norwegian Historical Data Centre (NHDC) is a national institution under the Faculty of Social Science at the University of Tromsų (UiTų). Their aim is to computerize the Norwegian censuses 1865 onwards together with the parish registers and other sources from the 18th and 19th centuries.
The National Archival Services of Norway (Riksarkivet) and the regional state archives (statsarkivene) together form the National Archival Services of Norway (Arkivverket). The National Archival Services of Norway is an independent government authority under the Ministry of Culture.
Family Search.org is a non-profit service sponsored by The Church of Jesus Christ of Latter-day Saints. The Church has been actively gathering and preserving genealogical records worldwide for over 100 years. In Oslo, the church has a large microfilm collection.