I have written a post before about installing Windows 8 RC on a VHD and dual booting it. Now Windows 8 RTM version is available (MSDN Subscribers) only at this point of time. General availability is expected on October 26th.
Steps to Install Windows 8 on a Windows 7 Box.
1. Open Device Manager from the Windows Control Panel or simply type devmgmt.msc from the command prompt or Windows -> Run.
2. Create a Partition by Shrinking the volume.
3. Specify the amount of space to shrink from the available space displayed.
4. Now specify a drive for the new Volume.
5. Create a Windows 8 Install Media. If you want to install Windows 8 from a USB Drive d ownload the Windows 7 USB/DVD download tool and follow the steps in the tool to load the image into the USB drive.
6. During the installation select the option to Install as a new install (Do not select Upgrade).
7. Install Windows 8 on the newly created volume (Step 4).
Now Windows 8 will be installed and you have the dual boot option to Windows 7/Windows 8.
- How to install Windows 8 on a Mac (lasdrashid.wordpress.com)