This solution is fairly simple. I do the following:
1) Stop the SQL Server service for the Evaluation Edition
2) Copy the databases from the \Data directory to a different directory.
3) Uninstall the Evaluation Edition
4) Install the Express Edition
5) Download, and install, the SQL Server Management Studio for Express Edition (off of the MSDN web site (msdn.microsoft.com/vstudio/express/sql/download)
6) Copy the databases back to the data directory.
7) Within Management Studio, attach the databases you just copied.
You're Done!
Hope this helps...
Scott Klein
Author - Professional SQL Server 2005 XML
http://www.wrox.com/WileyCDA/WroxTit...764597922.html