>Hi,
>
>Some weeks ago I installed SQL Server 2008 R2 Express on a customer server. During the installation I had to (probably since I don't remember) enter some Admin password to the SQL Server. Of course, I didn't write it down. I can connect to the SQL via SSMS using Windows authentication without any problem. But the customer is asking me for a password so that the DBA can set up a back up plan for the databases.
>
>How can I find out what password I entered? Or, where do I set up a password in SSMS so that I can give it to the DBA for his needs?

Don't. Trying to change the password for the sa account is troublesome and mainly unnecessary. You are the admin already, so create a login for the DBA and give him the appropriate rights.