I always thought that doing X11 tunnelling with ssh would be a hard thing to setup and understand but it turns out to be quite easy.
First of all on the machine being connected to (remotehost) change the sshd_config file to include:
then kill -HUP the sshd client.
Next when connecting from linux use the following syntax:
ssh -X remotehost
login as usual.
Now try a simple xterm & to see if it works. It went first time for me.
The extended entry contains the html from the page I found this. If it is still working you can reach it here. I copied the source over since this is being hosted on a .edu site and it will likely disappear once the student leaves school.