First we delete the entry for the standard X server

    * Click on the standard server that appears in the "Servers to Start" list
    * Click the "Remove Button" 

Now we create a new entry for the Xgl server

    * Click the "Add/Modify" button
    * Set the new server to use "VT 1". Use "Standard" for the "Server" option - this indicates which profile to use for the server, ideally we could create a new "Xgl" profile here but at the present time we cannot create a new profile using gdmsetup, so we'll just modify the settings for the "Standard" profile. Don't enter any options here. Click "Ok" when done.
    * Under "Server Settings" change the "Server Name" to "Xgl"
    * Enter your Xgl command in the "Command" box, for example, ati users would type: 

/usr/bin/Xgl :1 -ac -accel xv:pbuffer -accel glx:pbuffer