Recently had a client have issues with their WSS site and needed to restore the content DB. I took a look at their server and could not find the DB's. After a little investigation we discovered that they had attached to the Embedded Edition of sql instead of the Standard edition that was installed.
What was strange about this is the way the embedded edition works. I could not attach to it in the SQL manager. After some searching I found this method of attaching to it.
If you put this into the ServerName area it will connect. If you use the actual instance name for server name it will not work. If anyone knows some more about the above connection / server name it would be great if you could explain it.
On the same topic, it appears that WSS can run on the Embedded edition. However, I would not recommend it. To correct the situation we stopped the service. Grabbed the .mdf files and attached them to the standers SQL 2005 server instance and then ported WSS to use that Database instance.
Also, the instance name is listed as SERVERNAME\MICROSOFT##SSEE