for solaris 10 and below, there is a file /usr/dt/config/Xconfig
inside this file are configuration entries look for something which says.
############################################################################
# To disable listening for XDMCP requests from X-terminals.
#
Dtlogin.requestPort: 0
'#' it out and restart machine,
Solaris 10's.
1. Log in as root
2. Open a terminal
3. type gdmsetup (a dialog box will appear)
4 Click on the XDMCP tab
5. Check the Enable XDMCP box
6. Press Close
unfortunately for my case, my solaris8 box is already '#' out for the entry and it's still not coming
... investigating again.