Hi
Microsoft SharePoint Portal Server 2003 includes these databases:
1. _PROF
A profile database which contains SharePoint profile information for the Portal.
2. _SITE
A site database which contains all of the Portal information.
3. _SERV
A service database which contains the alert definitions and notifications, gatherer logs.
4. _Config_DB
The Configuration database which contains the server definitions for the farm environment.
All of these except site database can only have one for entire farm.
Microsoft Office SharePoint Server 2007 includes the databases list below:
1. Databases for SSPs
2. Search databases for SSPs
3. Content databases for each web application
4. Search database
5. Configuration database
For how to migrate databases from SPS 2003 to MOSS 2007, please refer to
http://technet.microsoft.com/en-us/library/cc263299.aspx
There is a reference with steps to migrate personal sites to MOSS 2007 which will be helpful to you.
http://blogs.msdn.com/jingmeili/archive/2007/02/26/how-to-migrate-sps-2003-my-sites-to-moss-2007-using-the-same-web-app-hosting-the-portal-site.aspx
Best Regards!