Attempting to install an older version of Windows on top of Windows Vista is not as simple as it may appear. “A disk read error has occurred. Press CTRL+ALT+DEL to restart” is the error message that the users will receive. There is an issue with the way the setup process in older versions of Windows handles the boot sector on the primary Windows Vista partition, and this problem is the source of the error. This happens because, if you take Windows XP, for example, the setup process will attempt to overwrite the boot sector on the Vista partition.

“You can install Windows XP over Windows Vista. You need to perform few steps before you can get both the OS running. Earlier versions of Windows used to parse BOOT.INI to load Operating Systems. Windows XP and earlier NT-line technologies use NTLDR as their boot loader. In Windows Vista, it has been changed and now Winload.exe is the boot loader for all the operating systems. This exe is invoked by Windows Boot Manager (Bootmgr.exe),” Microsoft revealed.

According to the Redmond Company, the issue is related to the NTLDR and BOOT.INI in Windows XP and Winload.exe and Boot Configuration Data in Windows Vista. This is because Microsoft has modified Windows Vista in order to support API call.

“Windows Boot Manager reads the Boot Configuration Data and displays and operating system list. Boot Configuration Data replaces the BOOT.INI used in previous versions of Windows. Boot Configuration Data is stored in a data file in C:BootBCD. Boot Configuration Data can be altered by a command line tool (bcedit.exe) or using WMI script,” reads a fragment of KB 555852.

And follow this link if you wish to manage problems with Windows Vista and earlier version of the Windows operating system in a dual-boot configuration.