Seriously, it all boils down to how good the camera feels in your hands, and which camera's button layout makes more sense. Does your dad have pretty big hands? If so, the Rebel isn't really a good choice unless he likes the small size.
I prefer Nikon's because they're generally larger and IMO have better ergonomics. I don't have to flip through menus just to change the common things on my D70, and I have 2 command dials on both the front and rear of the body to change aperture and shutter speed independently. Rebels have one dial that does a whole bunch of things and ultimately ends up being a bit crowded IMO, you also have to slow down and go through the LCD menu to change your WB, ISO, IQ, and other common adjustments. One of the main purposes of an SLR is the fast operation, and whatÂ’s fast about flipping through pages of menus to change your WB and ISO? On all Nikons, just hold down the ISO, WB, or IQ buttons on the back and turn the rear dial. Done.
I really like my D70s. It does 99% of what I need it to do and it feels great when I got my 80-200mm on it. I've used an XTi with the 70-200 f/2.8L and it was not fun. The balance was way off and there was no way to comfortably hold it.
The best thing you can do is go into town, go to camera shops that sell both Nikon and Canon, and actually feel, hold, and use them. DO NOT go to Best Buy or Circuit City to test them out because they have been used and abused, and have the big wire braces on them to protect against theft and they get in the way and totally alter the balance of the bodies.
Also, megapixels don't matter. My D70 will make just as good prints as an XTi. I've made 20x30 prints off my D70s and they come out stellar. I'm seriously considering printing the picture of the first boat in
this thread to a 12x18. Any SLR will make an amazing image, It's mainly up to the technique of the photographer and the optics. I've made 12x18 comparison prints from a Rebel XT and my D70 and the only way you could tell a difference between the two was becuase the XT white balance was a little off because unlike most Nikon's, Canon Rebel's can't do white balance fine tuning.
And for God's sake, PLEASE DO NOT buy a silver SLR. Not only will you look rediculous, but nobody will take you seriously because of it.