I'm no expert on this, but my basic understanding is that you generally want two lights, on either side of the background (not at 90 degrees to it), aimed towards the center, far enough back to illuminate evenly, and angled downwards to reduce spill. Continuous lighting is probably better for this, or at least makes it easier to ensure that you're correctly lit.

In terms of lighting modifiers, it will depend. If you can control the strengths of the strobes sufficiently, you might not require them. That'll probably require some experimentation. In generally, your background light should be about a stop less than your foreground.

Anyways, that's a nutshell summary of various articles I've read and hardly an exhaustive tutorial on the subject. For further info, unless we have a real lighting wizard pop in here to fill in better details, you might want to look at what videographers do, it's the same principle just at more frames per second.

Also, as a final tip, make sure your subject isn't wearing something matching the key. Unless, of course, you're looking to partially remove them. :)