I'll echoe Cowperson's comment,
The most important thing to know is that you are responsible for making great pictures, not your camera! Given that, if you need excellent resolution and detail then an dSLR is the way to go. The bigger sensor just gives you a far cleaner image, especially in low light.
It's also important to remember that you're not just buying a camera, you're really buying a system that will include lenses, flashes, etc... If you have a friend who shoots with a particular system, it may be a good idea to buy that brand too so you can borrow their equipment. I shoot Nikon because my friend shoots with it so we exchange equipment all the time, I don't need to buy that wide angle lens or macro lens because he already has them.
The good thing is that both Nikon and Canon have an excellent range of lenses to choose from, you really can't go wrong with either one.
I don't know your personality but if you are one to get frustrated easily you may want to take the classes. I know a lot of people who buy dSLRs and then get frustrated because they can't figure out the controls, and then they lose interest. Take the class and your learning curve will be much shorter and quicker. On the other hand, there is so much information available online if you want to learn on your own. The already mentioned dpreview.com has a decent community if you ever need help.
And finally, the D40 for sale in the Buy/Sell Forum is mine, let me know if you are interested. It's a great camera and the image quality is fantastic. Unfortunately I used to have a D50 that was stolen, it was just perfect for my hands and I want to get back to that, or possibly upgrade to the D80.
300S