debian fully automatic install

What you want is the "preseed" functionality of Debian installer.

http://wiki.debian.org/DebianInstaller/Preseed

Basically, you create a configuration file with all installer questions answered, use that file to compile a special kernel and boot it (or you can create a CD ISO image). Details in the Debian wiki (link above).

You'll have to create different preseed configuration files to differentiate between installations, I'm not familiar with a way to differentiate based on MAC address of network device.