Actually, when I use su - to become root and then run gpe-package, gpe-package refuses to run. It produces an error message which says:
(gpe-package:4777): Gtk-WARNING **: cannot open display:
I suspect this means that root has no default X display? Or something? I'm out of my depth here
When I use su to become root (no -) and run gpe-package, it works, can install things, and occasionally pops up the occasional, seemingly harmless message about how ldconfig didn't work to do something or other.