Here’s how to do it,
First of all download the Vistart app make sure that you skip the additional optional downloads while installing the app).
After installing the app you will get the Start button on the taskbar,but it will overlap with the first pinned taskbar icon.
The Start button overlaps the Internet Explorer icon to fix that issue,you have to create a new toolbar using the following steps,
Create a New Folder on Desktop
After Creating the folder you need to Right Click on the Windows Taskbar >Toolbars >New Toolbar to create new toolbar from the menu
Browse through the newly created folder and select the folder.
Now right-click on the taskbar and uncheck “Lock The Taskbar”option from the menu.
This will unlock the Taskbar so now you can move the “New Folder” Taskbar element anywhere on the Taskbar,so position the element to the Start Orb.
Now right click on the taskbar element “New folder” which is under the Start orb and uncheck the “Show Text” and “Show title” in the menu.
Now you have the Start Button and the Start Menu running on your Windows 8 Consumer Preview :)
A origem e as capturas de tela estão localizadas aqui