Just click any of the icons representing the old Windows Start Menu (orb) or Windows Metro Style. After that click Restart Explorer and that is all.
You'll have old windows start menu (orb) in Windows 8, but it will also disable Explorer with ribbon and taskmanager. You can also return to the new windows metro style menu.
Please note that Windows 8 Start Menu Switcher needs to be run with administrative privileges.
Windows 8 Developer Preview is available for download via this page.
Here are some key features of "Windows 8 Start Menu Switcher":
· Run at startup, so you can change it anytime you want
· Hides on system tray (notification area)
· Only works on Windows 8
· special button to only enable/disable old windows start menu, requires admin privileges