There are a few significant differences between the D80 and the D200, but onlya few.
The D200 uses CF cards while the D80 uses SD Cards.
The D200 can bracket the exposure in finer increments and in more shots.
The D200 can shoot 5 frames per second, while the D80 can only shoot 3 fps.
The fastest shutter speed of the D200 is 1/8,000, while the fastest in the D80 is 1/4,000.
The D80 has a Retouch menu that the D200 does not. (Nikon presumes that, with the D200, you'll be doing your post processing on a computer, whereas, since the D80 is more of a consumer dSLR, there's a greater chance you'd be printing straight from the camera.)
The D200 can bracket the flash in more shots.
The D200, naturally, is intended more for the professional, than is the D80 (but the same could be said about the D80 when compared to the D40x.)
You can compare them yourself at http://www.nikonusa.com/fileuploads/...SLRCompare.pdf