Hi, How you proceed really depends on what kind of end result you are looking for. If your goal is to have the whole floor re-finished and looking uniform throughout, then you really don't have any other options but to sand down the entire floor. You can rent the same equipment that the pros use, but you will wish you had just bitten the bullet and had them come and do it. The pros use large drum sanding machines that start with very rough grit and then progress to a finer grit with successive sandings. THey end up removing about 1/8 to 3/16 (or more) of the top thickness of the finished floor boards. This is basically done the same weather you are refinishing a 30 year old floor or a 200 year old floor. They do the edges with edge sanding machines while on their knees. They collect all the dust as they go and smooth final sand everything. Then they set all of the old nails (if it is face nailed). For the best results they should make a paste with some of the sawdust and fill in all of the cracks (before the final sanding) if that is the look you want. They then put their 3 coats of finish on the floor. The entire job should take them 3 days start to finish - one day for sanding and 2 for 3 coats of poly. If you try do do it this way (the right way) yourself then you will probably not do it right and the amount of work involved in huge. It will take you at least twice as long as the pros and remember, this job makes your house basically unlivable. You will be best off camping in the backyard for a couple days or staying at a motel or with friends. I am an experienced carpenter and foreman and I tried doing this myself on one of my small jobs (16' x 14' floor) and it took way too long and really beat me up. You will only really be happy with biting the bullet and having it done right. These guys do this every day and they are very quick and very good at it. I would only use someone who gives you several local references where you can (and should) go over and see their work and talk to the people. Like anything else, there are fly-by-nighters who will take your money and leave you with a nightmare.
If you don't have the money to do it as above, then you might want to get nice big rugs and just re-poly the edges. You will probably have to spend more on rugs than on a pro floor refinisher. Good Luck!