what kind of pictures, though. d200 is a good high speed cam, capable of 5 fps, for 22 consecutive RAW files, at the expense of an older, smaller sensor. the d90 has a newer sensor, which i'm presuming has better lowlight capabilities, despite being a slightly denser sensor, with only 4.5fps, and i'm sure it has a smaller buffer, so definitely no where near as big of a burst. http://www.dpreview.com/reviews/compare_post.asp?method=sidebyside&cameras=nikon_d90,nikon_d200&show=all
here, this will give you more of an idea of what each has over the other.