1. Prescan the 2003 Sharepoint site or database using the following command in 12 hive directory:
Prescan /all : for all sites.
Prescan /v http://SiteUrl : For a single site.
2. Check the logs of prescan, if any errors fix it and prescan again until operation completes without errors.
3. Take the backup of database.
4. Restore the database in Sql Server 2005 at MOSS 2007 environment.
5. Create a web application in central administration (MOSS 2007).
6. Open the command prompt and change to 12 hive directory.
7. Use the stsadm –o addcontentdb Command to upgrade the database:
stsadm.exe -o addcontentdb -url
It takes time(hours) to upgrade the database depends on the size of database.
That’s it, Operation completed successfully. If not check for errors in log file(Upgrade Log).
Note : SP1 should be installed at Moss 2007 environment before upgrade.