Performing a Database Migration
The database migration upgrade is best when you are changing hardware as well as upgrading SharePoint. For example, if both SharePoint and SQL Server are hosted on the same server, you can use this approach to move the content database to a dedicated SQL Server for better performance. (SharePoint and SQL Server compete for memory, so using a dedicated SQL Server usually results in better performance.)
Database migration is also the way to go if you want to leave the existing web application in place after upgrade process. Using this process, you can host both the pre- and post-upgrade web applications on the same server. To switch from one to the other, you simply stop one web application in IIS and start the other. You can even use the same URL for both web applications as long as only one is running at a time.
To perform a database migration:
Run PRESCAN.EXE on the web application to upgrade. Prescan must succeed without errors in order to be able to upgrade the web application.
Set the web application's content database to read-only to prevent changes during the upgrade process.
Copy the existing content database to a new database.
Create a new WSS 2.0 web application and attach the copied content databases to that web application. You can do this on your staging server if you have one.
Verify that the new web application works as expected.
Upgrade the new WSS 2.0 web application to WSS 3.0. You can use the in-place or side-by-side upgrade procedure.