Is It Possible to Set Up Dual Boot for XP 32 Bit and XP 64 Bit on the Same Hard Disk?
Absolutely yes! You can set up dual boot for XP 32 bit and XP 64 bit and even put up multi boot for Windows Vista 32 bit and Vista 64 bit as well as Windows 7. And for the matter, you can also set up multi boot for previous versions of Windows as well. This may sound confusing but the boot.ini file of XP can take care of multiple boots: not only the dual boot Win XP 32 and Win XP 64 but also previous (up to Windows 2K) and later versions up to Windows 7.
The only conditions to be considered are:
A) There should be a separate partition for each of the operating systems you wish to install - be it dual boot or multi boot.
B) The older version should be installed first.
Reasons for above conditions:
[A] The reason for having a separate partition for each of the operating system is simple: you won't want your copy of Windows XP 32 bit to confuse program files (My Programs) and data folders (My Docs etc) with program files of XP 64 bit. Even you too can differentiate among these folders easily if they are located on different partitions.
[B] The boot.ini file is resident on the system folder, which is on the C drive in most cases. The boot-loader file, NTLDR, studies the boot.ini to interpret the location of system files. If you install a newer version of Windows first and then an older version, the NTLDR may not be able to interpret the location of older operating systems and will eventually lead to a system crash. In other cases, you do NOT get any dual or multi boot. Only the default (latest) OS is available on the computer.
OFFBEAT: There is no NTLDR for Windows' versions prior to Windows 2000. Even then, if you wish to create a multi-boot including Win 98SE, you can have it. The only thing is that you won't be able to incorporate more than two operating systems when working with 98SE as primary OS. The boot-loader in 98SE cannot handle more than two OS at a time in most cases.
MULTI-BOOT COMPUTERS: In a multi-boot scenario, you can install Win 2K first and then Win XP 32 bit, then Win XP 64 bit and so on. This way, you make sure that boot.ini has all correct pointers that help NTLDR locate the system files to load the OS you want to use. In other words, if you start from Win2K, you can get a healthy, working multi-boot system. If you want to multi boot Windows 7, you have to reverse the process as its boot loader will not recognize XP after you install Windows 7.