I've used a Nikon D40 AND a Canon 400d(aka XTI). I basically learned on my Nikon D40, which is a great camera for people who are making the switch from a Point and shoot to a DSLR. I find that the menu's and interface on the Nikons are easier to learn on, especially the D40. I recently upgraded to a Canon XTI, just because I wanted some of the features that it has that the Nikon didn't. Plus I can swap lenses with my friends who own Canons. Both cameras are great, but it's not just the camera that makes the picture, so before you go out and pick up a nice camera, I would learn on a camera that you already own. (For me that was a Canon A95 point and shoot a few years back).
Photoshop also helps.
I'm selling my Nikon D40 by the way. It comes with the kit lens, a 2 gig card, a carry bag, a 50mm f1.8 lens, and all the original packaging/paperwork/warranty card. The thing with D40's is that it only has the ability to autofocus on AF-S/AF-I lenses. Most people don't use autofocus while shooting macro(which is what most of us who take pictures of our tanks do), and it still Autofocus's with the majority of lenses that a beginner would use (kit lens 18-55mm, 55-200mm, etc).
