Hello,
I agree with Rimmer on using the
GIMP. I would also recommend that you check out
InkScape. It's an Open Scource, scalable vector graphics program (SVG) that allows you to import popular image formats and create high quality vector images. It will also export files in PNG,(a popular format that supports layers and transparent type images) so if you plan on using the images on the web your covered.
The vector type graphic will allow you to scale images, and keep the same high quality because instead of coloring by the pixel, it uses math coordinates to specify coloring regions.
Note: There are free Photoshop plug-ins that also work with the GIMP, and will add more commands to use on images.
Hope this helps,
nos