GIMP has the features & capability of Photoshop. However, if you think Photoshop's interface is not intuitive GIMP may create despair (I will admit that as a long, long-time Photoshop user I've succumbed to subliminal interface training and expect other graphics apps to look & work like Photoshop 'cause thats how they should')
Check out gimpshop, a fork of GIMP which changes the layout of the user interface to resemble PS. (http://freshmeat.net/projects/gimpshop/)
/Morten