I recently embarked on a quest to migrate a client from a Windwos Small Business Server 2003 implementation to the latest and greatest Small Business Server 2008. Initially upon reading the documentation from Microsoft it seemed like it wasn't too tough of a task. I later found that this was NOT the case. Essentially, the client had just purchased a Dell PowerEdge T605 server to be the host of the new SBS 2008 server. To make a long story short, Dell pre-configures their servers (OOBE) to load their specific hardware drivers and what not. This posed a problem as the SBS Server 2008 would not then read the sbsanswerfile.xml (it must be named this) once you booted the new server up. It would launch into the stand alone installation and would not read the USB or CD-ROM media containing the answer file. To try and get around this, I tried several ideas from various news group posts all of which failed for my scenario (pre-configured server). I had done three seperate installs burning several precious houts when, finally, I came across the solution... with one caveat - if you don't perform the operation at the right time during the installation you risk missing the opportunity to load the answer file and it will be too late and there isn't any way to go back or tell SBS 2008 to look for the answer file on subsequent screens.
Basically what needs to be done on servers with a pre-configured OS installed is a simple little command line trick. Essentially, the following screenshot is the most important screen and where you will open a command line to perform the simple trick:
Press Shift + F10 and you'll get a standard windows command line. Then you can save your sbsanswerfile.xml to the local C:\ drive. I burned the answer file to a CD-R and place it into the CD-ROM of the new server. I CD'd over to the CD-ROM drive and then did a COPY statement from the CD-R to the root C:\ drive. That's important - it has to be the root of the C:\ drive or it will not work. From there I removed the CD-ROM with the answer file and then I simply popped in the Windows SBS 2008 Installation disk and continued installing and Voila! It finally picked up that I was wanted to perform a migration. Afterwards, it successfully joined the new SBS 2008 server to the existing domain (something that doesn't happen with a standard install) and started to pull the Exchange mail boxes and AD users over to the new server.
A huge benefit of using this method (among many others) is that it allows for an extended period of 21 days for both the SBS 2003 and SBS 2008 to be on the same network/domain without violating the license agreement or causing reboots/shutdowns for either server (normally 7 days without migration). This gives sysadmins time to transition things over with enough room to breath! Kudos to MS, although I wish there was a way to just select the answer file through a standard windows dialog box to make things easier. Hopefully this will help others who are experiencing the same issue with a pre-configured server unit. I didn't find much on it using Google, so maybe some desperate admin's will find this to be of use.