B - you don't know shit about cameras do you....
Anyway, pertanent to the thread:
XT vs XTi - The XTi has a nice sensor auto cleanign function and its 10.2mp as opposed to 8.2. It would be very comperable, its just a little new technology...probably worth the extra $$. Since your wife is Japanese I assume she probably has small hands. However, if the XT/XTi is too small (a lot of people complain about how small the body is) you could pick up a used 20D body for about the same price as an XTi. Word of warning, once you get her a DSLR, she's going to want more lenses. I know I spend way too much time drooling over glass now that I have an XT. If you're also looking for a cheap replacement for the kit lens, look at the Sigma 17-70mm lens. I just got one, its sharp as hell and only about $350.
Now for the controverical debate...
Canon vs Nikon
Personally, I have had bad luck with Nikon gear. My parents 1st digicam was a Nikon P&S that was not very good quality at all. The coating on the lens was all messed up and would create wierd artifacts.
Canons have lower ISO noise than Nikons. This means that in low light you'll get images that are less grainy and well...noisey. Canons also tend to have a greater selection of glass available, and its also cheaper.
Personally I would choose an XT body and then get her a nice lens too. You could pick up an XT body for arround $500 and then get a Canon 17-40mm F/4L lens for $650. Or you could go the cheaper rout and get a Sigma 17-70 f/2.8 for $350 like I mentioned before.
Anyway, if you REALLy want to get good information, stop posting on hondaswap and ask some questions on the
POTN Forums. The people there really know their shit. A lot of pro photographers hang out on the site. Realize its a canon forum so it'll be a bit biased....but then again, Canon is the best!