He may be referring to the DISPLAY environment
variable. This variable (on the system you log
in to) needs to be set (and exported) to the
IP address of your machine (the one you are
running "rx" on). However, if you are going
through a firewall, this will probably not work
unless the firewall is open on the X11 ports
(this would be a BAD thing!). If your organization
uses VPN access then it should not be a problem.
If not, you can still use SSH and X11 port
forwarding. You should check with your admin
folks regarding this.