hi,
try to use "rlogin sun_ip -l sun_user" with "xhost + & set display 'local_ip':0.0", but before do that you would close you firewall on fc first.
good luck.
Re: How can i get access to a SUN workstation under Fedora C
you can use ssh or telnet to access sun workstation.
if you want run some X program, be sure change the settings of FC3 that allow TCP connecting in the property of the display item of the menu.
then you can use xhost and export DISPLAY to run X program.