Updating XDarwin to Work with Mac OS 10.1

If you have an older version of XDarwin that doesn't open up under Mac OS 10.1, download http://prdownloads.sourceforge.net/xonx/XDarwin1.0a3.tgz

cd ~/Desktop [or wherever your browser is set to put downloaded things]
su [and type in your root password]
cp Darwin1.0a3.tgz /
cd /
tar zxvf XDarwin1.0a3.tgz
rm XDarwin1.0a3.tgz

For more details see http://mrcla.com/XonX/

Upgrading from Mac OS 10.0.4 to Mac OS 10.1 also overwrites the /etc/ssh_config file, so even if X-forwarding worked before it is now broken. Go back and put the following lines at the end of /etc/ssh_config (or uncomment and edit the relevant lines):

Host *
        ForwardX11 yes
        Protocol 2,1

Finally, type "exit" to get out of the root login.