I suggest waiting until around the end of Feb for Canon's announcement of a 300D replacement. If it sounds good, get it. Hurry up and get itbefore Nikon releases a D70 replacement
More seriously, another option is to go to a store and handle a D70 and a 300D/10D/20D (and 300D II if/when possible) -- look through the viewfinder; focus on objects near/far, shoot / focus as quickly as you think you might want to for real. That should tell you a lot to help make up your mind. Don't handle cameras you can't afford. Do expect to spend hundreds on lenses (in the long run) if you're really picky about image quality.
Any of those cameras can get the job done after all. Cameras had enough features in them (together with knowledge / external light meters, etc.) about 50 years ago.
The 20D is a much faster camera than the current 300D. But if you're shooting / composing slowly, this doesn't matter. If you want to shoot 20 frames in a minute, it does matter. Most people don't really need to shoot 20 frames in a minute, and the results are pretty boring when they're all the same.
On a vacation, I used a 17-40 f/4.0 L for around 90% of my pictures. I used a 70-200 f/4.0 L for the other 10% -- really only for shots of distant animals. Wide angle is harder to get right than telephoto. As I can only speak about Canon from experience, though IMO the Nikon's a finecamera, if I had to makethis decision for myself, I'd probably get a 300D II (when it's out) and a 17-40 f/4.0 L, an external flash (probably 3rd party E-TTL II + manual with tilt & swivel). If I couldn't afford the 17-40, I'd just get the kit lens.Then wait a few weeks / months as needed and get the 17-40. Later add a 70-200 f/4.0 L or perhaps a Sigma 70-200 f/2.8.
The kit lens is surprisingly good, but it's not great. It's worth the $100 or so. But it's also worth considering a less compromised lens.
I wish I could say that the 50 1.8 would be enough to start and an alternative to the kit lens. But with the affordable DSL crop factor, it's a bit too much telephoto for general purpose usage -- it's more ofa portrait lens. It is a great lens optically which is quite affordable.