The GNU Image Manipulation Program allows you to create, edit, and manipulate images. It can also be used as a paint program, since it has drawing and painting tools. This presentation is a very simple introduction for beginners; a more advanced GIMP presentation is planned for a meeting in the summer.
(Note: For those of you with a decent Internet connection, The GUM (GIMP User Manual) has recently been updated, and can be found in HTML and Adobe PDF form at http://manual.gimp.org/. The PDF files are 9.6Meg for the manual and 1.2Meg for the colour plates...)