What's the difference between all the newer Nikon Cameras (D40, D40x, SLR, D3000)?

I'm looking to buy one of the Nikon D series cameras but I don't know what the difference is between them. I was looking at the ones that are in the $400-$800 range such as the D40s, 80s and specifically the 3000. What do they all mean. What is the difference and what does SLR mean? Can someone help me out here and simplify this stuff. And no I don't need a less advanced camera I'm learning slowly but surely I just need help here right quick.

Here's a good place to begin your research.
http://www.bhphotovideo.com/...video.com/

I bought the new Nikon D3100 and I can tell you that is a great camera. The full HD 1080p videos are Kristal clear and the photos are just wonderful. This camera also has some fun built in photo editing like fisheye effect or color outline… And the most important part: it has continuously auto-focus so if you shoot something that is moving the camera will focus on it till he get out of the frame witch is a great tool if you shoot sport events.

You can pick up a used D-40 with a warranty and save a lot of money that you can use on a second lens. All the cameras will take photos, and since you are learning on digital you are not going to pay for processing to see your mistakes. I learned from my dad who was a pro with his own studio, and he made me carry a notebook and write down the apertature and the shutter speed and the ASA (ISO) for each shot if I pushed it.

All current SLR cameras share two things in common. 1) flipping mirror behind the lens 2) interchangeable lenses

The numbers that follow the "D" on Nikon DSLRs are just there to differentiate or name their models, but have no meanings in themselves on the 'level' or 'quality' the cameras are.

The difference is in their price, and features. A more expensive camera may have features- such as better build quality, faster shooting, and video recording- that cheaper models doesn't. This of course depends on specific models you're comparing.

If you are looking for a first DSLR camera that falls between the 400-800 range, I strongly recommend you take a look at the new Nikon D3100, which was just made available not too long ago.