First, you need to have a clean white background, preferably seamless paper. BTW, white seamless comes in two flavors - color and B&w (believe it or not). The color is the "normal", the B/W has a little more phosphor in it to make it look whiter, to aid in "dropping out" the background for this kind of shot in B/W. Now I haven't seen it for a while, but they did make it for a long time. I only get color anyway.
Second, you need to get the lights on your background at least 5 feet from the background, and at least a couple feet behind the model (more is better on both of these). You should use 4 heads unless you have something like umbrellas to soften it and give it some spread. Then - very important - get some large black foamcore or something solid, to flag the spill of the background lights and the lights themselves (especially wtih umbrellas) to hit the model, and especially the camera, and also to soak up the stray white light bouncing all over the place. Contrary to previous opinions, the background should be between 1/2 stop and 1 stop over the reading on the model. Any hotter and you will get flare in the camera from the bounce-back off the background. The background is already white - you can't make it any more white than that. (I usually settle on 2/3 hotter than the model). If the light is soft, it will flow down to the model's feet and reduce the shadow.
If the model is far enough in front of the background, the main light can be almost anything you want. One or two umbrellas or a softbox. In the shot of Jaime Bergman below, the main light is one large (8' tall) softbox off to one side, about 4 feet away. The was no fill light or reflector on the other side. There was still some bounce back from the background, which means this background was still a bit too hot, but it did flare nicely and give some wrap around her body. And there is no retouching around her feet.
Obviously one thing you want to do on these kind of shots, basic catalog stuff as in the other shot (front lit by two even softboxes), is keep the contrast in your subject. There are three ways to keep this from happening: 1) Don't overlight the background, 2) Keep your lens clean, 3) Keep the model larger in the frame to give the backgound less image area in which to blast. Some photographers I know also build large black foamcore frames around the whole set, like a proscenium in a theater, to reduce the bounceback from the background.
I personally wouldn't get too anal about keeping shadows off the floor from the model's fee. Imagers have been retouching those out for years, long before Photoshop made it really easy. (Being on white paper meant the graphics people could do it in the printing process). In fact it is so commonplace that when I do catalogs we no longer make an effort to keep footprints off the paper, or change paper when it gets dirty, its easier to clean in Photoshop.
Andy Pearlman Studio