I'm having this problem with the installer installing on a Dell Dimension 4500 with a Realtek NIC. It detects the NIC, but still fails. I was running Debian Etch before this with no errors, so I know the NIC works properly. Any idea how to get around this without replacing the NIC?
[!!] Postfix Configuration
Installation step failed
An installation step failed. You can try to run the failing item again from the menu, or skip it and choose something else. The failing step is: Select and install software