Up until now I’ve been using the EBSPrepTool and recommending running it, but there’s a better tool now, called the IT health scanner
Run it on your SBS 2003 before you being the migration
And tattoo this blog post to your forehead and DOUBLECHECK these potential issues before you hit them:
http://blogs.technet.com/sbs/archive/2009/02/19/sbs-2008-migrations-from-sbs-2003-keys-to-success.aspx (you can also go to www.sbsmigrationtips.com )
So far I’d say THE biggest hit the wall event that nails people and they should use this tool ahead of time to ensure they don’t hit the wall is the journal wrap error. When you have a SBS box, and you have a dirty shutdown, you can end up in a situation where the AD won’t replicate properly. In a single DC environment we won’t notice until we go to do the migration.
How do we get dirty shutdowns? In my own situation at home I got it because PG&E shut down the power on the house and I didn’t have a UPS connected to the server. AD should be shut down nicely and gracefully, not with the breaker box turned off.