Agreed - if you plan to be using high ISO stuff regularly [indoor sports, etc] then D300 will be very rewarding despite the price tag. It also has more focus points [frankly, sometimes its too many], and has a few in-camera editing options that I never reallly use, live view - again, useful but only on are occasions as it uses batteries more intensively and I prefer the viewfinder, and 3d focus tracking - a feature i havent yet really had time to figure out. Oh there is also an inbuilt sensor clean function but as my sensor has shown no signs of dust yet I cant say how good it is.
The d200 is incredibly flexible and useable and a great piece of kit but is let down when high ISO comes into play. Not a problem if you are only going to be using it occasionally and there is plenty of good Noise reduction software available to deal with most of it.
Consider what ou will be doing with the camera then decide which is best for you - in terms of physical handling they are almost identical - a couple of buttons have moved on the 300 but overall very similar.