I was cloning some Ubuntu 8.04 LTS machines from a template i made and everything went fine, except the kernel could not find my eth0 and mapped a new eth1.
After some thinking and testing, i found out that the device manager’s had the old MAC address in the udev rules file. (ofcoz, doh!)
In pure happiness, i deleted the lines (except for the comments) in the rules file located here:
/etc/udev/rules.d/70-persistent-net.rules
and rebooted. and BUM! the network is running perfectly and the persistent rule file is regenerated.
Helpfull reading on udev:
http://www.linuxformat.co.uk/includes/download.php?PDF=LXF66.tut_udev.pdf
/Renzo