We had this question a few days ago. Use search. And just to give you a short answer: No. You can't. The menubar is not the equivalent of Windows' taskbar, rather that'd be the Dock, which you _can_ autohide. The menubar is more like the menubar in Windows, you know 'File', 'Edit' etc., which you normally can't autohide. But other than in Windows, the Mac's menubar is global and always visible (with the exception of some applications like games).