uhhh the d90 is pretty much a d300. you'll get a larger body and a couple other small features, but you'll also lose a couple features as well. in most areas, the d90 is a superior or equivalent camera to the d300. i just paid $1300 for a mint but used d300. i would think you could easily get enough out of selling both of your cameras to get a d300, but honestly your d90 should get just about any job done.

and to be completely honest... google is your friend. just sayin'.