this is caused by setting the boot volume to not be readable by "everyone" To avoid this problem DO NOT change the permissions of the drive. Instead, just dont share the drive.
If you have ssh running, you can ssh into the system, and run "chown 775 /" (as root) that will restore the read privlage for "everyone" The login window will pop up on your server.
If ssh is not running, just reinstall from the install disk. and then run the updaters again. You wont loose any of your netinfo stuff.
You might have a problem at the setup screen where it starts looking for a bootp server. You can only cancel this in the first second or so, so you have to be quick.. If you miss it, it will keep looking forever. You'll have to do a hard boot and start again.. this time dont miss the cancel buton once it starts looking for a bootp server.
These are both known problems with Apple (I know, I helped them figure them out...) Its a bit of a pain in the @#@@, but once you know, it is simple to fix/avoid.
Hope this helps.