Make a Copy of a Microsoft SQL Server 2005 database from a Mirror Copy
I agree this should be moved to the dba stack exchange, though since I answer there as well I will post it here should it be migrated.

The only way to access a mirrored database from the mirror server is through a database snapshot, which will require enterprise edition of SQL Server. It will also be READ ONLY, so this may not work for what you want.

The other alternative is to take the backups of the primary (these, I would hope, should be available) and restore them for your use somewhere else up to the time you need.

If using already taken backups is not possible, ask for a copy_only backup to be taken on the primary and given to you.