If your wallet can afford it why not get a Wacom graphire tablet? Not only are they great for painting and drawing (the pen is much easier to use than a mouse) but it comes bundled with Photoshop Elements 1.0 and Painter Classic which I know from experience is a fantastic paint app. It's very easy to learn and use.
I believe the tablet is about $150 in Canada.
Carbon has a refurbished wacom Graphire 2 for $107.+ change. I bought one for my daughter a while ago and, as adagio stated,it's bundled with Painter Classic and Photoshop El. Painter is my favorite app.
The Paint module has always been the weakest part of ClarisWorks/AppleWorks. There are freeware paint programs on the Web that will run circles around it. GraphicConverter, which is actually a conversion program, has a simple built-in paint program that is infinitely superior.
If you want to step up further, find an old copy of Photoshop. You should be able to find version 3.x for $50 or so, and that will give you about 75% of the power of the current version for most purposes. For $150 or so, there's Photoshop Elements, which is OS X compatible in the current version.