"Cannot connect to X server" whilest telnetting to another UNIX system
From a Fedora Core 1 system terminal window on my gnome desktop, I'm trying to telnet to a Sun UNIX system and run emacs (or any other X-based program). On the Sun, I get "emacs: Cannot connect to X server 10.3.1.40:0.0", but no emacs. The IP address of my Linux system on our local network is 10.3.1.40, so I know DISPLAY is set properly on the Sun, and I've run "xhost +" on the Linux system before telnetting to the Sun, so that's not the problem either.
I'm on a local network in a hospital, and God only knows what the gateway I'm connected to is doing. I have no access to the gateway, and no knowledge other than "it's there and it's probably set to 'Paranoid' mode since we've had so many hacker problems in the past". To confuse things even more (in my mind), I can telnet from one Sun to another and run emacs just fine, it's just the Linux box that's not behaving. So, my question is, what exactly can I ping, probe, stat, cat, or check so I can fix this, or even determine whether it's my problem or a gateway configuration problem? I'm an old, grizzled programmer, but new to this depth of network system administration, so be gentle with me.
Thanks in advance,