If you're trying to restore a file from a Time Machine backup, just run Time Machine from the Dock. It will automatically mount the sparse.bundle image. (If it's from another machine or not your current backup, you can still use Time Machine to "browse" another backup. You can get to that option from Time Machine in the Dock either by click+hold, or right-click.)
Using Time Machine to access it is really the best way to access your TM backups.