In terms of image quality, low noise, and ease of use, the Nikon D-80 will be the Canon XTi. You sure don't really need that very expensive Nikor VR 18mm to 200mm. There are other great lenses out there for less money.
If flash is the issue. The Nikon SB-800 flash will beat any of the Canon Flashes hands down. I own the Canon XT and will be buying the Nikon D-80. Still need a bit of convincing: just read the February issue of popular Photography.