Go opensource, save yourself some money, and learn some great software while you are at it.
The suggestion for the
gimp is a wonderful one. If you are looking to touch up or colour in a scanned image or simply draw wacom style, that's the program to use. Also, if you are more familiar with Photoshop, check out
Gimpshop, a hack to make it appear and feel more like PS.
However, if you wish to draw directly in a program with just a mouse, I'd recommend
Sodipodi. There's a windows version out there (even though it can be a hassle to install-check out
this page to see how to correct the installation errors it provides). Sodipodi straightens your lines as you draw (much like Flash if you've used it).