There are three ways that I know of to enable other hosts to display x
clients on your screen.  In order from least secure to most secure:

xhost - xhost is host based authentication.  man xhost provides a
        pretty good explanation.  

xauth - authorizes individual users based on the presence of a 
        ~/.Xauthority file.  To set up basic authentication, as root:
           # cd ~
           # xauth
           xauth> add <your host name> MIT-MAGIC-COOKIE-1 <hex key>
        where <hex key> is a long hex digit.  It has to be of even 
        length.  
           xauth> exit
	   # cp .Xauthority /etc/X11/Xauthority
           # chmod 600 /etc/X11/Xauthority
 	Next, edit your startx script (startx for linux-pmac, not sure
  	exactly what for MkLinux) - in startx, change the line that 
	says:
		serverargs=""
	to:
		serverargs="-auth /etc/X11/Xauthority"
	Now, give a copy of /root/.Xauthority to any user, on any host
	who you want to be able to use the Xserver.  Changes will take 
	affect the next time you start X.

	Its probably a good idea to redo this process every once in a
	while, using a fresh key.

ssh -	ssh stands for secure shell, and is available for free at
	ftp://ftp.cs.hut.fi/pub/ssh/ 

	It provides functionality similar to rsh/rlogin, but all data 
	is encrypted.  It has many more powerful features, one of which
	being secure, encrypted, compressed X forwarding.  Its well
	documented, so once its installed + configured on a system level,
	all you have to do is "ssh -f -C host xwhatever" and it will 
	display locally.  

 Scott Lipcon
slipcon@cs.jhu.edu