I've recently figured out a problem when upgrading from 2.4 kernel to 2.6. It was because the 2.4 kernel detected my (in use) network adapter as eth0 while the 2.6 kernel detected the unused network adapter as eth0 instead. I had to configure eth1 to get the 2.6 kernel on the network.
1. Was it detected differently because of udev?
2. Can I force a network adapter to always be eth0?