One common request that has hit our forum (and inboxes) is how to bring back the classic start button in the developers preview. If you find that you want to experience Windows 8 DP without the new start button interface, follow the steps below to regain the classic start button functionality.
To get back the old start menu, open regedit, goto
HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionExplorer
change value of RPEnabled from "1" to "0"
close regedit, you get your old start menu......the catch is, no more metro UI because you just disabled it. To get back the Metro UI, change the value back to "1"
Howto: Enable the classic start menu in Windows 8
Posted on Wednesday, September 14 2011 @ 19:54 CEST by Thomas De Maesschalck
Neowin published a register hack that allows you to enable the classic start menu in the developer preview of Windows 8: