To get an elementary idea of the refinish-ability of your floor, you need to get a look at how much floor you have 'left' above the tongue-and-groove (assuming it's a tongue-and-groove floor.) Assuming it's T & G, remove a floor-mounted heating register (if you have forced hot air.) Then, get a mirror and hold it inside the duct. From there, you should be able to 'look back' at the 'end' of the wood strips to see how close the floor is to the tongue. If it looks like you have 1/8" or so, you can possibly refinish it. (A pro can tell for sure how much you have left.) Then, do the same at other registers/vents around the room. Also, sometimes, you can remove the 'transition strips' (if you have them) between, say, a dining room and a kitchen doorway to get a look at the wood from the side.
Unless you have a good idea of the sandability of the the floor, have a pro look at it. It's not that often that I hear of a T&G floor needing to be removed because there is no more wood to sand. (Usually, these floors end up getting covered w/carpet or something instead of being ripped up. That's OK.)