I just bought a house with a lot of hardwood flooring. The floors are in pretty good shape, but need to be shined up. The problem is that there are dark stains in every room from carpets or low furniture. The stains aren't that bad, but have distinct lines at the edges. I don't really want to completely refinish the floors unless I have to. Any ideas on how to spot sand or clean? The house was built in 1993. Also, what's the best way to clean the floors and shine them? How can I find out what type of finish is on them now? Thanks for any help.

Odds are you have some form of polyurethane floor finish. To clean and maintain the floors, read this:
http://www.hardwoodinstaller.com/hardwo ... orcare.htm

Also, I suspect the dark stains you are seeing are not stains at all but are the original color of the floor and the lighter areas are where the floor has been exposed to light. This will cause the floor to lighten up over time. It is common for floors to have outlines of furniture and rugs. The best remedy is to move things around to allow the floors to receive the same amount of light exposure. If you do not want to wait floor the floors to eventually even out (it could take 6 months or more), then your only recourse is to refinish all the floors. Spot sanding and restaining areas will not work.