D200 is essentially the same body shell as a D300 so if you have a shop nearby, I'd advise to see how it feels to you in the hand. It's a lot more substantial in feel to a D40 and as always suggested, how a camera feels to hold and is equally important to how much tech it contains.
Anyway, a D200 us a good buy. Mpbphotographic have a fair few in for mid-£300s. Solid, pro build quality, excellent IQ and a very sensible button and menu layout. With a grip it's excellent, although slightly taller than a D2/D3 and not everyone's taste.
I started out in Nikon with a D200 (used Canon xxD before that) and I loved it. DPS mag spreads looked great from the raw files and the overall performance compared to the 30D I was using, was miles better. Noise above ISO 1000 can be an issue if you underexpose but it's nothing LR3 can't sort out. AF speed and accuracy is excellent too.