This is coming from someone who switched from Nikon to Canon (mainly because of what I had to shoot).
I've owned a D70 and had a lot of experience with the XT.
The first thing I noticed about the D70 is that it handles much better than the XT. I like how it felt to the hand much better than the XT which was a little bit "narrower" to my hand. However, this is all personal preference so it may feel different to you, so I strongly suggest you try it out yourself.
The D70 controls were also much better than the XT's. I just didn't like having to navigate using the SET button and stuff every single time.
However, in terms of image quality, both are very similar until you hit the higher ISO ranges. The XT does not even compare to the D70 in terms of high ISO noise control. It is much better in handling noise than the D70, but Canon pretty much had the edge in that for quite awhile (especially during the time of these two cameras).
Thus, for low light photography where you may be using high ISOs, the XT is definitely recommended.
Thus theres sort of a balance here. If you don't take many shots that require the noise handling in high ISO ranges, then you may want the Nikon for the better handling (in my hands at least). But in terms of image quality, and versatility in that field, the XT is better. At least you have the option to shoot in low light, compared to the D70, where there's definitely no option there.
edit: I would also like to add, that if you already have a system of lenses from either brand that is compatible with the cameras you're mentioning, then I would definitely recommend sticking with that brand. It's quite expensive switching when you already have a system of lens, unless you're willing to take the time to sell them all privately.
That's not entirely true. Nikon has plenty of stellar long telephotos that are every bit as good as canon's, and then some. Canon no longer produces their ultrafast 200mm, Nikon has one with VR. Canon does not offer a long telephoto zoom like the Nikon 200-400 VR. On the cheaper side, people tend to like the nikon 80-400 VR just fine though I hear the 100-400 IS being panned a lot, and the Nikon 70-200 VR is in some cases regarded as having the edge in that area.
The problem with Nikon that I noticed when I was using their equipment is that they don't carry a good line of budget-line lenses in the telephoto range.
The last time I checked, for the 70-200s, they only offered one version, the 70-200/2.8 VR.
Canon has the 70-200/4L (both IS and non-IS), as well as both tastes of the 70-200/2.8L.
Thus, if you wanted that range, you would need to get the 80-200/2.8 or the 70-200, which are very expensive lens. A lot of amateurs usually don't have money like that, so it would have been great to have the f/4 versions that Canon been offering for a while.
The same applies to the wide lenses. Nikon doesn't even offer anything equivalent to the 17-40/4L for example. This is one of the cheapest high quality lens you can get from Canon, but it's still somewhat reachable by amateurs at least.
It all depends on the photographer, but one of the things I've noticed was that Canon really had lenses of high quality that could be much more easily accessible than the Nikon equivalents.