You could try "GIMP for Windows".
There are 4 parts to it.
1. GTK+ 2 for Windows
2. The Gimp for Windows
3. GIMP Animation Package
4. GIMP Help 2
WEBSITE
It is free but it was originally designed for Linux, which means it can be a bit confusing to use.
Useful plugin
PLUGIN DOWNLOAD PAGE
Haven't used it much I use photoshop CS but it is supposed to be good if you can figure out how it works.
