You can SSH to a server with X11 forwarding to allow you to run X11 (graphical) applications on the server and have them show up on your local machine.
ssh -X [the user]@[the server]
However, if you then run su to log in as a different user, you'll probably receive the following error when you run an X11 application:
X11 connection rejected because of wrong authentication. X I/O error
Prevent this error by exporting, after su, the authority you gave the initial user to run X11 applications:
export XAUTHORITY=/home/[the user]/.Xauthority