In my opinion I would put the Canon 30D in the same market as the Nikon D80. The Nikon D200 is more biased towards the semi pro , with many of the controls to hand to change settings on the camera, without dropping into menus etc. Not essential for most non pro's, but may be of benefit down the line if you ever take the next step ?
As stated by others there is not a massive difference between models & more time should be spent deciding which of the lenses you prefer, as this is where you will spend more of your money in the long term. This would then help you decide on which brand of camera to go for.
Some of these threads may help
CANON 400D, 5D, NIKON D80, D200, would you change....
Help with DSLR choice - Canon 5D, Nikon D200 ?
http://www.pixalo.com/community/came...ther-9548.html