The following are some resources that may be useful for a GIMP user. Unfortunately, many resources apply to older versions.
The GIMP User Group offers an informative and interesting Web site at http://gug.sunsite.dk.
http://www.gimp.org is the official home page of The GIMP.
Grokking the GIMP by Carey Bunks is an excellent book based on an older GIMP version. Although some aspects of the program have changed, it can provide excellent guidance for image manipulation. An online version is available at http://gimp-savvy.com/BOOK/.
http://gimp-print.sourceforge.net is the Web page for the GIMP print plug-in. The user manual available from the site provides detailed information about configuring and using the program.