If you install Windows 7 using the custom installation option and haven’t formatted the drive, you will have a Windows.old file from your previous installation. Some people are asking how do get rid of this file, since some are unable to delete it from their systems because Windows 7 may be protecting the file. One simple way is to use the Disk Cleanup utility.
Microsoft describes the procedure to remove Windows.old:
‘Open Disk Cleanup by clicking the Start button . In the search box, type Disk Cleanup, and then, in the list of results, click Disk Cleanup.
If you’re prompted to choose a drive, click the drive you just installed Windows on, and then click OK.
In the Disk Cleanup dialog box, on the Disk Cleanup tab, click Clean up system files.
If you’re again prompted to choose a drive, click the drive you just installed Windows on, and then click OK.
Select the Previous Windows installation(s) check box, and any other check boxes for the files you want to delete, and then click OK.
In the message that appears, click Delete Files.’
Before you use Disk Cleanup, make sure that all of your files and settings are in Windows 7 where you expect them to be. Deleting the Windows.old folder can’t be undone.
I would also recommend that you backup the file if possible to DVD. Just my 2 cents.