Setting up and starting GNOME or other GUI on Solaris 10

Not in a million years should you be doing XDMCP over a public network.

Why not use VNC ?

X11 is SSSSSOOOO network heavy.  I personally haven't used XDM in years - too many security issues relating to its use.  I use the following script as my VNC xstartup script.  In  my .profile (or whatever) I create a ENV variable called DEFAULT_WM with a value of my preferred display manager tweaking the script as necessary.

Depending on where I'm setting it up, I may have the Solaris machine setup to block everything except incoming SSH and then tunnel VNC traffic through it or I'll leave it open (like here at home).

#!/bin/sh
# $XConsortium: xinitrc.cpp,v 1.4 91/08/22 11:41:34 rws Exp $

userresources=$HOME/.Xresources
usermodmap=$HOME/.Xmodmap
sysresources=/usr/X11R6/lib/X11/xinit/.Xresources
sysmodmap=/usr/X11R6/lib/X11/xinit/.Xmodmap

# merge in defaults and keymaps

if [ -f $sysresources ]; then
    xrdb -merge $sysresources
fi

if [ -f $sysmodmap ]; then
    xmodmap $sysmodmap
fi

if [ -f $userresources ]; then
    xrdb -merge $userresources
fi

if [ -f $usermodmap ]; then
    xmodmap $usermodmap
fi

# start some nice programs

case ${DEFAULT_WM} in
   # TWM
   [Tt][Ww][Mm])
      /usr/X11R6/bin/twm &
      xclock -geometry 50x50-1+1 &
      xterm -geometry 80x40+223-97 &
      xterm -geometry 80x40-42-0 &
      exec xterm -geometry 80x40+0+0 -name last-process
   ;;
   # ICEWM
   [Ii][Cc][Ee][Ww][Mm])
      /usr/X11R6/bin/icewm &
      xclock -geometry 50x50-1+1 &
      xterm -geometry 80x40+223-97 &
      xterm -geometry 80x40-42-0 &
      exec xterm -geometry 80x40+0+0 -name last-process
   ;;
   # KDE
   [Kk][Dd][Ee])
      exec /usr/local/bin/startkde
   ;;
   # Gnome
   [Gg][Nn][Oo][Mm][Ee])
      exec gnome-session
   ;;
   # Enlightenment
   [Ee][Nn][Ll][Ii][Gg][Hh][Tt][Ee][Nn][Mm][Ee][Nn][Tt])
      exec enlightenment
   ;;
   # Blackbox
   [Bb][Ll][Aa][Cc][Kk][Bb][Oo][Xx])
      # File must be setup for wheel group with read-only group priv and
      # I must be member of wheel group for xconsole to work.
      xterm -geometry 80x24+0+16 &
      xterm -geometry 80x24-14+16 &
      #wmnd &
      #/usr/local/bin/bubblemon &
      exec /usr/X11R6/bin/blackbox
   ;;
   # XFCE
   [Xx][Ff][Cc][Ee])
      startxfce4
   ;;

   # Fluxbox
   [Ff][Ll][Uu][Xx][Bb][Oo][Xx])
      # File must be setup for wheel group with read-only group priv and
      # I must be member of wheel group for xconsole to work.
      xterm -sl 5000 -sb -geometry 80x24+0+16 &
      xterm -sl 5000 -sb -geometry 80x24-14+16 &
      #wmnd &
      #/usr/local/bin/bubblemon &
      if [ -f /usr/local/bin/display ]; then
         exec fluxbox
      else
         exec fluxbox -rc ${HOME}/.fluxbox-noDISPLAY/init
      fi
   ;;

   *)
      echo
      echo "Put the crack pipe down and step away from the computer ..."
      echo "You either ran startx without an argument or the window"
      echo "manager you want to run is not configured in your .xinitrc."
      echo "Check windows managers available and update your .xinitrc"
      echo "accordingly."
      exit 1
   ;;
esac