Run GUI application as another user.

I knew that if there is some flaw in irc-client it will leave a security loop in the system. And the attacker get the privilege of the user running the irc-client. And you know what it will lead to.
So specially to run the X-chat (a irc client), I created another user irc with very less privilege.

Then I tried running the xchat as follows:

suraj $ su irc
Password:
irc$ xchat
No protocol specified

(xchat:6966): Gtk-WARNING **: cannot open display: :0.0

Hum.. There occured a problem. The app couldn't get handle to the grapics display.

So here is the solution:

$ sudo apt-get install sux

and run

$ sux irc xchat
Password:

Provide the password of the user irc and see the application launching.