What price range should I look at to get away from kiddy point and shoot to a nice camera? I'm not looking to spend over $500 if possible
Since you have your budget set, paruse craigslist and find a good deal on a used one. That is where I got mine, and I got a pretty good deal on it a few years ago.
but when it comes to like the Nikon D40s, D60s , D90s, I don't really see the difference except cost...
The amount of pixels, and features. For instance, the D40 does not have a focusing motor, so it will only auto focus with certain lenses that have the motors built in. Not a big deal if you are really wanting to get into photography and learn to do it all yourself, but a lot of people who just want a fancy pants camera dont like it. Also, IIRC the D60 and D90 have two finger wheels, you can use them to adjust two different settings at once, for instance you can use one to adjust aperture and the other for sutter speed. Also, the image capturing unit gets better with higher end models. This can help reduce image grain when shooting with higher ISO's.
Also the Canon EOS Rebel looks nice... Is there really that much of a difference between a $100 8mp point and shoot and a $350 8mp SLR ?
Yes there really is that much of a difference.
FWIW I like the D40, it is cheap, and a great place to start. Has all the features a begginer or even an experienced shooter would want. It's drawback is the lens issue that I mentioned before, you
may end up paying a bit more for glass if you end up keeping it, but you can ALWAYS upgrade the body later if you want, and keep your lenses. I have heard good things about the Canons too, but dont have any personal experience.