And most tutorials for a good deal of work-alike programs (PS, PSP, etc.) will work with slight alteration in GIMP...
Actually, the Gimp is nothing like Photoshop, or anything similar. And that is a good thing, in most cases. Also, Photoshop plugins will not work in it. However, it is a high-quality program worth learning. The Gimp is a very nice program for fast web graphics.
http://www.xach.com/gimp/tutorials/
More Gimp stuff (http://www.vlug.org/linux/links/Graphics_-_2D-3D/GIMP/)
and, as was said, a google search will bring up a lot of good stuff for it.