I'm a new linux user and was reading the gimp manual, experimenting with gimp as I read. I soon ran into a problem. Gimp requires Alt+click to select a mask in the layers dialog. http://manual.gimp.org/manual/GUM/layers.html#913365 At the time I didn't know if the bug was in gimp or if one of the windowing systems (xfree86, enlightenment, gnome) was eating the input. Eventually I found the configuration file for enlightenment and was able to remove the Alt+click binding that was tied to moving a window. Since enlightenment is the default WM for redhat and since gimp is installed by default (its on the menu) shouldn't they work together by default?
Turn on your Scroll Lock to pass Alt keystrokes to The GIMP.