I don't know about installing Windows 7 to a new drive from the windows old folder however one option you could do is revert to Windows 7 from Windows 8 and then install Windows 8 to a different partition and dual boot the two OS.
You can revert to Windows 7:
Even though you cannot uninstall Windows 8 Consumer Preview, you can begin your restoration process by clicking “My Computer” first on the Start menu. Once you’re there, double-click the” Local Disk C: “and locate the “Windows.OLD” folder. If the ‘Windows.OLD” folder does not exist, you cannot proceed to Step 2. What you have to do is first create a back-up disk. Then you can transfer or restore your files into your old OS.
Once you have located the “Windows.OLD” folder, right-click it and choose “Properties”. This will help you determine how much free space the “Windows.OLD” folder has. If the free space of the “Windows.OLD” folder is larger, then you may not be able to restore Windows 7.
Insert the Windows 7 disk or USB and restart your computer when prompted to begin the installation process. Step 4: When you see the Install Windows Box. Select your preferred settings which include the language and time. On the left side at the bottom, you can see the prompt “Repair your computer”, click it.
Once the dialog box System Recovery Options appears, click Windows 8 Developer Preview and then click on Next.
After clicking on Next, you will see the Command Prompt. Click that because this is what you are going to use to restore Windows 7.
More details here.
Once you've reverted you can then create the new partition to install Windows 8 on a different drive that will not overwrite Windows 7. You should then be given an option at startup on which OS you want to boot.
NOTE: If you bought the Windows 8 PRO UPGRADE you can't have two seperate installations of Windows 8 and Windows 7.