There are official instructions on how to install Debian on http://wiki.debian.org/DebianOnFreeRunner, and the announcement.
Previous, partly now outdated information on how to install Debian manually has been moved to Manual Debian.
As with the standard OpenMoko distribution, you can ssh into the device over USB using
$ ssh root@192.168.0.202
The password is blank. You should change it right away
# passwd
To make suspend available you have to install apmd:
apt-get install apmd
After that you can suspend your phone with:
apm -s
and make it wake up again with pressing the power button.
Wuth 06:28, 17 August 2008 (UTC): I found that apmd was already installed by using the official debian installation procedure, but that the kernel didn't support apm. I haven't yet resolved this issue.
The default time zone is UTC. Reconfigure it by running
# dpkg-reconfigure tzdata
Set the clock manual using, e.g.
# date -s 00:33
That's probably not sufficient to keep the clock accurate. It might be worth configuring some form of NTP.