Most important thing first: the eLOM console lives on ttyS1 (9600n8). If that gets you going you do not need to read any more.
This works pretty easily, but there's isn't much information about how this works if you don't like using a keyboard and a screen (having these things appears to be the norm for x86 hardware). But the X2200 comes with this "Embedded Lights Out Manager" which, although not as good as the LOM on a T1000, does the job nicely. It allows you to connect via the serial console, IPMI and ssh. So initially I used the serial console to setup the IP configuration of the eLOM and then I could ssh to it (and more importantly sit in a quiter room far away from the rack).
Once inside the eLOM it allows you to connect to the "serial port" of the machine (with the rather obsusucre start /SP/AgentInfo/console command, disconnect by hitting Esc + Shift-9). This allows you to see the BIOS settings etc. Now is the time to insert the Debian CD (or netboot or whatever), if inserting the CD you'll just get a blank screen since it's displaying pretty graphics, hitting escape gives you the boot prompt as explained in the Debian installation manual. Now the serial console you're seeing will appear as the second serial port to the OS (this is configurable in the BIOS I think but I didn't play with those settings). So the correct way to start the installation is:
expert fb=false console=ttyS1,9600n8
(or "install" instead of "expert" if you prefer that)
This will start the normal install process you're used too (and which is described in other guides) with the output appearing on your terminal emulator. One tip tough is to enable the installation via ssh when it allows you to select the installer components to load. The serial console is 9600 baud and painting the dialog windows over that is just painfully slow, this is a lot nicer over ssh.
The last thing to note is that debian-installer is smart enough to enable a getty on the serial console you've used for the installation (if fact it doesn't enable any gettys on the normal ttys). But it doesn't append the console=ttyS1,9600n8 to the grub menu, so you'll want to do this yourself if you like seeing the kernel output on the console.