Migrating from SBS2003 to Exchange 2010

I have a customer who had SBS2003 server. Last year, they virtualized and brought up a bunch of 2008 R2 servers, one of them running Exchange 2010, which has been an adventure to say the least.

Last week, they asked us to add a new employee, which we did. However, she is not showing up in the GAL in Outlook, making things like delegation more difficult than they need to be. After hours of digging around, it seems that Outlook is still getting the GAL from the old Exchange 2003 server, suggesting that the migration was never completed.

Without knowing exactly what has and has not been done in the migration, I'm not sure what I need to do to completely eradicate the last remnants of Exchange 2003 from the network so that Outlook will start using the GAL on the Exchange 2010 server.

The previous admin said something about things not working...