Well, now that I'm done with the floor I thought I'd write up a quick tutorial for those thinking of doing it themselves. Keep in mind, I'm no pro, just a do-it-yourselfer who has done this one time. Hopefully I can pass along some good tips, but certainly don't consider this for your only source of info.
Read on for the tutorial...
Remove all furniture, baseboards, etc from the room. I also recommend removing curtains and any other fabric as you will generate a lot of sanding dust. Empty the closet, even if you don't plan to refinish the closet floor.
You need to make sure you either have a subfloor underneath the hardwood, or a thick enough hardwood floor that it can handle being thinned a bit. Once a floor is too thin, you'll chance cracking boards in the future when you move heavy furniture around.
The first thing you'll need is a drum sander. Check with your local hardware and equipment rental stores. If you've never used one before, I'd highly recommend renting one from a smaller hardware store or rental shop, as the guy at Lowe's or Home Depot probably doesn't even know how to turn it on, much less instruct you in it's use. Make sure you get a sander that runs on 110 current, because they do make larger ones that require 220 volts and are much harder to use.
Here's a nice before picture that has the sander as well: