The SBS 2008 getting started wizards assume that the server will be in a Class C subnet (i.e., subnet with a mask of 255.255.255.0). Furthermore, when you run the Connect to the Internet wizard, the wizard specifically looks for your Internet gateway at specific addresses in the 192.168.x.x class C subnet. So what if you’re migrating from an existing SBS 2003 server that doesn’t match one of these assumptions?
In the case of your existing server being in a subnet other than 192.168.x.x, no problem. When you create the answer file, you’ll plug in the IP addresses for the existing server, the IP gateway, and the new server into the Answer File Creator so that the migration setup can do its job. In the case of a new installation, the Connect to the Internet wizard will fail to automatically detect the router and you’ll be able to enter the information manually.
But if your network is on anything other than a Class C subnet, migration is not going to work. You will have to temporarily configure the network into a Class C setup to get the initial migration working. After that, you can modify the network settings to go back to your other network configuration, but the migration setup requires a Class C configuration in order to work.