Sql-server – How to change SharePoint database authentication

There is an annoying limitation of WSS3/2007 that prevents you from attaching the same content database more than once on an entire installation - the ID for the Site Collection is unique, and these are used as primary key in a table in the Config DB (shared for all web apps). You can get round this by either a) attaching the Content DB somewhere else (inconvenient), or hacking the offending table in the Config DB (potentially dangerous, although I've done this a couple of times with no ill effects); see SharePoint Things for details.

An easy way to see all your databases (and what web application they belong to) is to go to Central Admin -> Operations -> Perform a Backup.

This will give you a tree view of your farm with all of the databases listed.