I will soon have a registered company here in Norway. Is there any way I can offer some sort of confirmation to foreign customers so they know for sure it's a certified, valid, registered company? (In plain English of course)

I plan to include my hosting offers, webdesign, programming, server administration, computer building and repair into this company, and I want to make sure that foreign customers can verify that I am 100% serious with this.

Any ideas?

Nothing special. you could setup some legal documents, include the business registration number for your company. Reg No. #.... You will have this?

Yes, it's a Reg No that can be looked up in "Brønnøysundsregisteret" as it is called here in Norway, a business database consisting of all businesses registered here.

How do I setup these legal documents? I need to contact a lawyer?