http://www.ambientdesign.com/artrage.html
ArtRage is a painting package designed to provide a realistic and fun simulation of using paint on a canvas, along with pens, pencils, crayons, and other tools. You can run ArtRage on a normal Windows machine with a mouse, but it works particularly well if you have a graphics tablet. Even better, running ArtRage on a TabletPC takes advantage of the unique interaction of pen and screen to produce a realistic painting feel.

ArtRage is all about playing with paint without the mess, and having fun in the process. You can paint your own image from a blank canvas to completed work, or load in a picture to trace and have the tools pick their colours for you as you paint over it.