OK, I'll try...
I don't know of any sites that offer drawing guides, but there's been a lot of good advice from the professionals in the TLZ interviews
recently. And check out the 'how to draw' features on the seasons 3 and 4 discs, they're official stuff from the animators and very handy, even if you don't follow their drawing style.
The important thing to begin with is to get some practice sketching the characters. Lots of practice.
If you have your own particular drawing style that you're good at, it might be worth trying to draw the characters in that style, but I still think its good to get a feel for the groening style to start with.
About computer programs - These aren't always needed to create stunning artwork, when you're just starting out concentrate on the pencils, and worry about the digital crap later. Oh, and get a graphics tablet, it makes things much easier/ quicker.
The main high-end program that everyone uses, it'll do anything you like, but takes some getting used to. When learning it, concentrate on getting the hang of layers and the pen tool, as well as all the different colouring modes (multiply etc.)
Adobe Illustrator and Macromedia Freehand:
Perfect for turning a messy pencil drawing into smooth clean lines, it looks great, but I find it really boring to use, you might want to get some advice from a passing scan artist on using bezier curves and things, I can't explain them very well.
There's other, cheaper programs out there too (not that 'buying' software has ever been a problem for me
), paint shop pro is a good alternative to photoshop, and I've seen some rather nice artwork done in Corel Painter and Open Canvas, which both give a more hand-painted look. Although you might want to just use actual paint instead...
Take your time with your work, try to think of some cool idea for an artwork to motivate you to draw it. Watch the show a lot, and check out (but don't copy) other fanart to get some ideas. And finally, don't feel like everything has to be a masterpiece, it won't be, I'm quite happy being an average artist as long as I can get the ideas I have on to paper.Wooo! 500 posts!