I recently migrated a customer from SBS 2003 to SBS 2008. I've done a few of these. There is no in place upgrade as SBS 2003 is 32 bit and SBS 2008 is 64 bit. Because of this I've recommended to my customers to stay with 2003 until they replace their existing hardware. The migration is easiest if you're moving to new hardware at the same time. This time I decided to give the Swing method from sbsmigration.com a try. I'd heard a lot of good things about it. Last year I met Jeff Middleton, the owner, at an SBS event at Microsoft. I was impressed that the MS guys seemed to respect his deep knowledge of SBS. The Microsoft way is a series of documents and help files that walk you through installing the new SBS 2008 server in migration mode which joins it to the domain. Then in a series of steps you move Exchange, Sharepoint, user data, third party programs, and everything else that's on the old server over to the new server. Once this is complete you decommission the old server and clean up active directory. The Swing method is a little different. You create a third server, promote it to a domain controller in the existing SBS domain, then physically remove it from the domain. You migrate from this temporary domain controller to SBS 2008. This allows you to use the same server name, IP address, and other settings that the old SBS 2003 server used. This can greatly ease migrating some Line of Business applications. It also means you save a lot of time with the workstations. They essentially think it's the same server only with Exchange 2007. With the Microsoft method you have to touch every workstation as the new server has a different name and IP address.
To keep a long story short the Swing migration worked great on the customer's server. I did have a problem when I ran a test migration with my own SBS 2003 server. Here is where sbsmigration.com really kicked butt and why I now recommend it over the Microsoft way. Jeff's support was excellent. He was answering emails within minutes most of the time. Even on a weekend evening with him being in a time zone three hours ahead of me he was still answering emails. The problems I was experiencing were totally of my own making. As this was just a test I took a few shortcuts. My SBS server has seen many experiments over the years. Just recently I was testing IPv6 and had removed IPv4 from it for a while, I've had Blackberry Enterprise Server installed on it – things like that. The server is a bit of a mess let alone Active Directory. Jeff was very patient and helped me through my problems. I eventually gave up on the test migration as I was running out of time and I had learned enough to comfortably go ahead with a live customer migration. I picked up the customer's server on a Friday afternoon and returned Monday with the new SBS 2008 server. It took 17 hours over Friday evening, Saturday, and Sunday, then another five hours Monday at the customer's site. It was by far the cleanest SBS 2003 to 2008 migration I've done. Jeff's documentation on how to clean up Active Directory both before and after the migration is excellent. Sbsmigration.com – highly recommended.