You can install GIMP 2.7 on Ubuntu 11.10 using the matthaeus123 ppa for gimp. GIMP 2.7 is an unstable development version. A stable version (2.6) of GIMP can be installed from the Ubuntu Software Center.
GIMP is the GNU Image Manipulation Program. It is a freely distributed piece of software for such tasks as photo retouching, image composition and image authoring.
To add the ppa and install GIMP 2.7 open a terminal window (press SuperKey and type: terminal) and copy+paste the following lines:
sudo add-apt-repository ppa:matthaeus123/mrw-gimp-svn
sudo apt-get update
sudo apt-get install gimp