I just told him to take a look at this thread. I think he has a CC login but not sure...hopefully he'll be along soon.
Basically he loves the D300, and has lots of lenses for it too. The fisheye he's used in that pic you mention is a Peleng 180 degree lens - there's a Peleng group on flickr who just post those bendy looking pictures! Peleng is a factory in belarus which makes optical equipment - you can buy their stuff on
ebay for significantly less money than any other western photographic company, and get good results with it.
I think to get the professional look with the D300 you also have to be very good with photoshop and do a lot to tweak the settings on the camera itself. There's a lot more which is adjustable on it (that is my understanding anyway). He's moved to that from a D70...