I still use my Nikon D70 that was getting old when I bought it 3 years ago and I don't think its ever really constrained me (though the D300 is starting to tempt me. Luckily, or unluckily, I simply can't afford it).

If you're planning to get it used, check things like the shutter count and condition to make sure there's nothing bad about the camera (i.e. if there's 50k shutter closures it'll probably die soon). You might also want to consider a Nikon D50 since you don't have an existing lens system. I'd try out both bodies (or their newer equivalents since I'm sure the style hasn't changed much) and see which one you like more. Lenses are fairly equivalent between Nikon and Canon.