There is a small, open air tourist bus called the Loretto Line that you can pick up by the old town central Plaza, takes you up Canyon past the art galleries, then up past the celebrity homes, up to the Museum Hill, then back around old town. Takes about 1 hour and 15 minutes and gives you a good overall look at what is available in Santa Fe, plus some history. Our guide was a local born.
You can rent a car while in town, but I see very little reason. The vast majority of interesting things are less than a mile apart and parking is not very easy. Cabs do exist, should you get real tired.
Hwy 599 is an awesome bypass around Santa Fe if you are heading north...traffic can be a pain, so this is a great time saver. You know what you see in this picture at Rush hour?? no cars