http://www.derekyu.com/?page_id=219
Just use the Next/Previous buttons : some links on the right are broken.
If you want more tutorials/inspirations, you must go on PixelJoint.com. There are a lot of pixelart gurus on this website.
http://www.pixeljoint.com/default.asp
The tutorials are in the Feature menu.
Pixelizing your drawing as Prinz Eugn suggests is a good way to start. But remember that you must remove some parts if you downscale a lot to have a readable sprite. And here begins the fun part of pixelart : optimization of the pixels to draw what you want with a limited number of pixels