Even if you are from a country outside the above mentioned areas, you might be excempt from needing a tourist visa to visit Norway. This page will let you know if you need a visa or not.
Should you still be in doubt, for instance due to your Irish residence status, you need to contact the Royal Danish Embassy's visa section for clarification, . The Danish Embassy in Dublin deals with visa applications and requests for all the Scandinavian countries. You will find more information on their web site, Danish Embassy's visa page.
For more information about Norwegian visas, please go to the home page of UDI, the Norwegian Directorate of Immigration.
It is important to be aware that the online tool for applications found on the UDI homepage cannot be used for applicants in Ireland, as the Danish visa system differs from the Norwegian one. You will have to use the application tool found on the homepage of the Danish Embassy.