Karsten has an "Ultra-Mini How-To" on XDM under Debian [link|http://kmself.home.netcom.com/Linux/FAQs/xdm-disable.html
|here]. This may be useful to you :)

I'm in the process of being a convert myself...installing potato on my laptop as I type this (woody choked on install, a quick gander at the maillist archives proves my problem to be a known bug).