I have downloaded windows 8 developer preview. I have mounted its ISO, but it does not ask to choose a partition to install.
There might be a way (using some command line perhaps) to install windows 8 to another drive from within XP


Solution 1:

If you are talking about installing Windows 8 on a Virtual Machine over a Windows XP host, the answer is yes, you can do it using Virtual Box or VMWare.

If you are talking about installing Windows 8 upgrade from Windows XP the answer is no, you can't, actually you can only upgrade to Windows Vista from Windows XP, even on Windows 7 you can't do it.

Solution 2:

You have to boot into Windows 8 DP from startup. you cannot simply mount an ISO in an existing OS or it will overwrite the drive that the OS is installed on.

Solution 3:

You CAN do a multiboot Install without clearing anything

  • Download the ISO file from Microsoft.
  • Mount the ISO using Daemon Tools, Clone Drive, or similar.

(This is important. Do not use the autorun installer. The autorun installer only allows you to upgrade your existing Windows installation and will not allow you to install to a separate hard drive or partition.)

  • Navigate to the virtual install disc and go to the folder called sources.
  • Run setup.exe and proceed as if installing Windows Vista or 7.

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Links:
http://www.ghacks.net/2011/09/14/how-to-install-windows-8-from-usb-key/
http://techspyre.com/how-to-directly-install-windows-8-without-cd-dvd-or-usb/
http://www.reddit.com/r/windows/comments/kf7ax/installing_windows_8_without_bootable_media/