slackbuilds/system/gksu

GKSu is a library that provides a Gtk+ frontend to su and sudo.
It supports login shells and preserving environment when acting as
a su frontend. It is useful to menu items or other graphical
programs that need to ask a user's password to run another program
as another user.

The root terminal used when gksu is called from the menu defaults to
Xfce's terminal, but if you want something different, do something
like this:  TERM_APP=xterm ./gksu.SlackBuild

This requires libgksu.