To go a little more into it, Painter is one of the most amazing software products on the pro market today.
Basically it lets you turn your computer into a canvas. You can paint with any number of brushes, on any number of canvas types, and control colors and factors like how "wet" your watercolors are, how your brush affects the paint, how strong gravity is or how the water or paint flows down (or UP!!) the canvas.
Con: This is one of the most incredibly complex programs I've ever dealt with, but the control you get out of it is incredible. Try Mac Design magazine, they do some really cool stuff with painter. If you were to open every menu in Painter 7, you could easily fill up my 20" LCD with nothing but menus and not have any room for your canvas!!!
If you have a chance to use it, go for it. Just don't get discouraged, buy a book!!