a simple solution to prevent xdm from starting everytime you boot is to remove xdm from /etc/rc2.d. See, whenever linux boots it runs a script that causes the files in /etc/rcN.d where N is a number between 1 and 6 (called runlevels). Debian is set to runlevel 2 by default so by removing xdm from the directory executed in runlevel 2 you stop xdm from running at startup. This is a pretty crude way of doing it compared to some stuff that was discussed earlier this week, but its what i did and it works fine. (yea, that's exactly the same e-mail i sent earlier, but it applies here too, i think:)
