I've done mine several times and it is alot of work.
You can either use a drum or vibrating sander. The drum sander takes off more material, faster and is needed if you have cupping/warped boards, if they are badly scratched/gouged or if you want to change the stain color. It is an art to use a drum sander and takes practice. You can really damage a floor if you are not careful.
The vibrating pad type sanders can't do much damage. They are only good for scuffing up the surface, fixing minor scratches and a recoat of finish. My opinion!
Either way it is dusty and hard work.
As far as finishes I personnaly like the sweedish finishes...solvent based, not water based, I believe they are tougher and will last longer. You will need a proper resperator to use these. They can rip your lungs out. What ever type of finish you use be sure to check it's compatability with what is on there, unless the old surface is completly removed.
If you are a perfectionist and/or want a near perfect job...look in the yellow pages and get a quote. It is more expensive, but probably worth it in the long run....Joe

Most metropolitain areas have cheap refinishers that do a much better, quicker, and even cheaper job than you would.

However, I have done it myself (not a pro), mostly because I want to control the sanding finish and the materials I use to apply.

There are plenty of websites and books available on how to do it. You should refer to them.

As for products:

Stripping: Use a belt sander or a toxic-chemical remover. The environmentally-sensitive, water-soluable removers have not worked well for me on floors, and left residues/splotches that caused all sorts of problems.

Sanding: Rent a big machine that is new. Get a finishing sander for small parts.

Finish: I prefer using a danish penetrating oil first, then an oil-based polyurethane. The danish penetrating oils do a fantastic job of highlighting the depth and character of wood like no other product does. They come in natural (no color except a slight darkening) and various colors. They also serve as a good first layer that will not raise the grain and thwart all your sanding efforts. (Water-based stains and finishes tend to raise the grain). I then top the oil finish with an oil-based polyurethane (can't use water based poly over an oil finish), using either a tiny-thin mohair roller or a mohair pad applicator. Thin it a bit to ensure a smooth finish, and work quickly. DO NOT re-roll a smooth section that has sat for five to ten minutes or you will get lumps or (worse yet) air bubbles.

Finally, do not underestimate how long it will take you. Without the experience of a pro, you will **** up lots of time trying to figure things out, and you WILL make mistakes, which will at best delay the project way beyond the weekend (or two) you plan for it.