I thought it should be simple...
Follow the directions on line :
put the files in either the system-wide plugins directory /usr/lib/gedit-2/plugins/, or in the user plugins directory, which may need to be created, ~/.gnome2/gedit/plugins/
eg, I copied the file for codecomment(from the gedit-plugins package) to both(either) of the two directories above, but none of them works. I also tried other plugins and chmod the file & directories to 755, still can't load new plugins after restart gedit..
Thanks for the help~