Practically zero difference between 8MP and 6MP, and anyone who says otherwise exaggerates a lot.
I've seen the proof at some website. To double the number of horizontal and vertical pixels, you'd need to QUADRUPLE the number of MP. So a top-of-the-line 16 MP Canon provides 2x the number pixels along length and width when compared to a 4MP camera. It's a big deal to pros who do large prints, but not for us. Instead of photos that are 3008 x 2000 pixels (D70s), you're gonna get 3423 x 2304 photos from a Rebel XT (numbers taken from sample images).
Lets assume that MPixels is a non-factor. The Canon still provides photos that are less noisy because it uses a CMOS sensor instead of a CCD that every other company uses. It's a big deal when taking certain types of shots (eg: at night if I set the camera to ISO 1600, which is a setting to adjust the chips sensitivity to light), but the noise difference won't be massive.
However, if you didn't notice by holding it, the Rebel feels like cheap plastic poo. It's even prone to fingernail scratches. I know, I know.....WTF!?! It's too light and too small. I'm a guy with average size hands and the Rebel isn't comfortable.
The Nikon D70s produces more noise, but this is only a problem in certain situations, and the noise difference isn't ginormous because you'll have noise in both images. The kit lens of the D70s is better. The build is clearly better. It's more comfortable in most people's hands. You change the settings by turning those circular dials on the back of the camera and don't need the LCD to do so, and I
MUCH prefer this method. The Nikons have a longer battery life.
Too bad it only transfers photos to your computer at USB 1 type speeds, while the Rebel XT and similarly priced competition out there use USB 2.
After thinking about it for a long time and holding both in my hands, I'm going to change my mind and buy the Nikon D70s instead. A camera is only a tool. You still need to USE the camera that you buy, and I'm guessing that the D70s will be better to use. Rebel XT photos will be less noisy at high ISO, but
your photo quality will be poor with BOTH cameras if you don't learn about the settings, and that's what is going to make the difference.
If you hold the Rebel XT and D70s, and think the Rebel XT is still good, then get the Rebel XT. Many people are happy with it.