Completely agree with Jackal. Get a car and don't sweat it. If you're visiting on the weekend, don't miss a visit to the Wildlife Conservation Center, just a few minutes down the road from Girdwood at Portage. (Not sure when they go to winter hours but probably by November.) Watch out for moose while you're driving around Anchorage, especially in the dark. They're big and not car-friendly at all.