It works the same way in linux. Actually Xsun is based on X.org's X11, which is also based on XFree86 that redhat uses so they are pretty much the same in every aspect. If you mention the exact problem we may be able to help.
XDMCP is disabled by default under redhat. If you cd to /etc/X11, and grep for "XDMCP" in the files there, you'll find that there's one variable in one file that needs to be set to "true" in order for these connections to work. I'm sorry I don't remember which file/variable combination off the top of my head
The administrator has disabled public write access.