Once you've loaded the Windows 8 ISO on your flash drive, boot to that drive. (If your system bypasses the drive and boots straight into Windows 7, you may have to do some tinkering in the system BIOS. Not every PC will boot from a flash drive by default.)

This is the only really critical part of the process. After accepting the installer's software license, be sure to choose , not Upgrade. Next you'll see a list of available partitions; click , then select the unallocated space you created earlier.

Now, click from the drive options icons. By default, it should display the full amount of the selected partition, in which case go ahead and click .

Finally, click Next to begin the installation process. This will take about 20 minutes, after which your system will boot Windows 8 and run you through the usual initial-setup stuff. (You might have to remove your flash drive so the installer doesn't try to run again. It did on my system.)

From now on, when you boot your PC you'll see a start-up menu that gives you a choice between Windows 7 and Windows 8 -- and it'll proceed with booting the latter by default. If you want Windows 7 to remain the go-to operating system, click while this menu is visible, then click . Easy-peasy.