You have to configure your debian to start on runlevel 5 it's on the file '/etc/inittab' then you have to configure your X to start only on runlevel 5 and not on 3 it's simple, you have to rename services that you want to start like 'S99gdm', if you don't want it to start as 'K99gdm' or you can use the program 'sysv-rc-conf' easy to get on apt-get to do this symbolic links and renaming for you then you use, as root 'init 3' and 'init 5' to restart you X as you want
-- Henrique G. Abreu [EMAIL PROTECTED]