We decided to rent a car in Skagway. Avis is the only rental car company in Skagway. We got a full-size car with unlimited miles for $70 total. We have the car the from 8AM to 6PM. We thought this was a much better option than doing any of the White Pass excursions with the cruise line. Our excursion will be for about 8 hours longer and for much less. From what I understand, it's very difficult to get lost because the White Pass Highway is one road (unless you turn off). We're taking maps just in case.
The train is indeed excellent. I have done both the drive and the train. Andrew is in error, There are 2 rental companies out of Skagway- Sourdough- but they do charge .30 a mile for miles over 100. It is also not the White Pass Highway but the Klondike Highway. Few turn offs, and the rental companies will not allow the Tagish loop since it is not paved. Whitehorse is a bout 2 hours north but the scenery is only until Emerald Lake about 75 miles. Stop in Carcross and visit the small visitor center- a great streach break stop. You definately need to book ahead.