Once the process is finished, you can see the virtual hard disk among the other disk in the list in the lower half of the window. Right-click on the part that says Not initialized and choose Initialize .

Now, the status of the disk will list its memory as unallocated. Right click on "unallocated" and choose New Simple Volume .

Click yourself through the dialog, format the drive as NTFS and have a drive letter assigned to it. Now you have a mounted and ready to use virtual drive to install Windows 8 to.

Start it up, click on Apply . Under Source locate the file source.wim on your Windows 8 installation disk. As destination locate the drive letter of the VHD.

Click Apply and GImageX will extract Windows to the VHD. You can also click Verify and Check to make sure all files are written correctly and that the archive is error free.

Once the process is finished. Unmount the VHD by going back to DiskManagement. Right-click on the disk and click Detach.

By now you have an installed Windows 8 on the VHD. You now have the choice what to do. You can use the VHD on your external drive turning it into Windows ToGo and allowing you to boot your desktop computer. Then you could run the Windows 8 installer and try to see if the installation works properly. You could also use ToGo to install Win8 manually to the hard drive by repeating the above steps but using your desktop hard drive as destination. You could also copy the VHD to your desktop and boot it there and be happy.

I will describe how to run Win8 off your external drive to boot your desktop enabling you to choose among the above options.