Dollar914 - A direct fit, it is not. In order to get it to fit you will have to potentially widen the channel for the magazine and cut the tabs in the side of the magazine well, or you'd need to procure one of the many (superior) detachable box magazine systems.
I was in the same boat you where, got my SPS DM from Cabelas without much thought on the whole DBM thing. Kinda left me screwed on stock options for the stock DBM. The easiest way to do this is to just buy a BDL stock and a different DBM system (Badger Ord, Wyatts, etc) and use that instead. I never liked the Remington DM as the follower had a tendency to tilt during use. Sadly, we are kind of screwed in that way, as you can't just install a BDL change over kit to an SPS DM because the feed lips that would normally be present in the receiver are milled out so the magazine can do that job. So either you do some work on the stock yourself, buy one of the SPS DM specific stocks (there are a few out there), or buy a BDL stock and some other bottom metal with a detachable box magazine system.
I went the extreme route and bought an AI AICS 1.5 stock for my 700 SPS DM. It includes a DM system, is a fully adjustable stock, and has an aluminum bedding block. The cost to do all of that with a standard profile stock is about the same. The AICS stock is at least all together and designed that way. Well worth the cost.
As for free-floating and bedding, the Wikipedia links are a great start but all you really need to know is that for the most part, a floating barrel is going to be more accurate than one where the stock touches it because the barrel's harmonics cause the barrel to move. Free Floating allows it to return to the same position each time without influence. Without it free floated, the barrel will have an influence (the stock) which means it may not stop in exactly the same spot each time.
Bedding seats the action into the stock and relieves stresses that can reduce accuracy. Aluminum bedded stocks have a big aluminum block running through the stock (like the AICS stock) which is more capable of handling the forces of recoil than the plastic stocks. This helps keep the action tied to the stock and help reduce group sizes. Bedding compounds help reduce stresses in the action that would cause the barrel to return to a different location after each shot. It does so by providing a 100% contact area for the action to the stock.