I have set up a separate partition for the 8.1 preview using the ISO file. I was expecting the install program to ask which partition to use for the install.

It didn't and started (what appears to be) a regular install, I assume in my Win 8 partition (which is the main partition)!

Is there something additional I need to do to get the install to do its thing in the new partition?

Hi,

It should be  same with the process of installing a new system, when you burn it to a DVD, then you can use it to boot from the DVD and select custom installation.

You can refer to this tutorial :

Install Windows 8.1 on separate partition & Dual Boot it with another OS

http://www.thewindowsclub.com/install-windows-8-1-separate-partition

Please Note: Since the website is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.

Thank you, Alex, for your response.

It makes perfect sense! I had been bypassing the DVD burn and booting from it! I was simply using the Mount option (Right-click on ISO file) and executing from my C drive.

I will try the DVD approach! Thanks again!

Bryan

Thanks again!

Burning to DVD first and then booting from the DVD worked like a charm! I now have Windows 8 in one partition and Windows 8.1 in another!

The install took something less than 45 minutes - less than I was expecting!

That's all well and good, but what about the numerous ultrabooks etc that come without DVD drives nowadays. Why can't we install Windows 8 to a new partition from an existing OS like Windows 7, which is what I'm looking to do.

That's all well and good, but what about the numerous ultrabooks etc that come without DVD drives nowadays. Why can't we install Windows 8 to a new partition from an existing OS like Windows 7, which is what I'm looking to do.

You can put the Windows 8.1 on usb drive and boot from USB drive. I had to test that on several of ultrabooks  as well.