The 350D is a good camera. As a rule, the "ranking" of the DSLRs goes (best is last):
Nikon D50/ Canon 300D
Canon 350D
Nikon D70
Nikon D70/S (slightly bigger screen than the D70)
Canon 20D
Nikon D200 ($1800)
Canon 5 D ($3200)
Then they go super expensive after that.
The differences between the D50 - the D70 aren't really that great for most people. It's kinda like getting the Honda DX vs the Honda EX. People will rant on and on about them, but it's like trying to compare processors: you can gripe about little things, but in the end they're all so kick-ass it doesn't really matter.
There are people on both sides of the Canon / Nikon lens fence. I'd recomend going with what you already have the glass for (otherwise which way you go doesn't really matter). If you have an EOS, go with the canon stuff. If you have a Nikon, go with the Nikon stuff.
One thing: Don't mess with any of the other DSLRs yet. They aren't even in the same league.