and in addition to restore headeronly you can also execute "restore filelistonly" to get a list of the database and log files that are contained in the backup set from which you are trying to restore.

Also discussion from the following URL may prove useful for you ( they are suggesting the same as what Gail suggested, namely the REPLACE option)

http://social.msdn.microsoft.com/Forums/en/sqldatabaseengine/thread/4f17d722-5c4a-4730-a2cf-1507b6e6be17

http://msdn.microsoft.com/en-us/library/aa238217(v=sql.80).aspx

http://blog.sqlauthority.com/2007/09/27/sql-server-fix-error-3154-the-backup-set-holds-a-backup-of-a-database-other-than-the-existing-database/[/url]