Laura,
We spent two weeks touring Norway in the summer of 2005. I would love to share travel tips...please feel free to ask away.
One thing I will say upfront, Norway and the rest of the countries of Scandinavia are very very expensive. Like, $12 for a glass of wine in a restaurant. $5 for a bottle of water in the store. A lunch of two hamburgers and two beers (one beer each) could cost $55 (that's what it cost us, in Bergen). Getting there might be expensive, but once you are there, be prepared to open your wallet and pour out money.
That said, Norway was beautiful, the people are friendly, and everyone speaks English. I would definitely go back.
We had a car (we bought our car in Trollhatten, Sweden) so I didn't have any experience with public transportation in Norway.
Where would you be traveling from? A few years ago, we got a very good fare on SAS from Newark, NJ to Stockholm (direct flight). You could then take a train from Arlanda (the airport near Stockholm) to Oslo. I believe they have high speed trains that make that trip.
Let me know what else I can tell you...
Leslie