Several features present in Windows 7 Professional are no longer there in Windows 8 Pro. Furthermore, the upgrade process gives you no warning that these features will be removed. Windows XP Mode is trickier to deal with than most. As you're no-longer running Windows 7 Professional, you won't be able to download and install it. Here's how to install Windows XP Mode on Windows 8.
Thankfully, the upgrade from Windows 7 to Windows 8 doesn't actually delete your Windows XP Mode virtual disk. The original XP installation is stored in a .vhd file, which you will usually find in "C:\Program Files\Windows XP Mode".
This is a clean installation of Windows XP and doesn't contain any changed you made to it, by installing programs or adjusting settings. A separate .vhd file contains your changes.
While most Virtualisation software runs just as well on Windows 8 as it does on Windows 7, you'll need a specific XP Mode version of the software to handle the activation of the XP Mode installation. Simply loading up the .vhd file with another virtualisation application won't work as XP will start up deactivated and won't allow you to sign in.
Run XP Mode in Windows 8
Download and install VMLite XP Mode and follow the instructions to import your Windows XP Mode installation. Once you've done this, you will have a working Windows XP Mode installation running in VMLite on Windows 8 Pro.
By default, the VMLite XP Mode installation will import the base XP Mode .vhd file, so you'll get a fresh install of XP Mode missing anything you installed or configured under XP Mode yourself.
To bring back all the changes and settings you may have made, you'll need to shut down the VMLite XP Mode virtual PC and change its settings so it will use your differencing VHD file instead of the clean one imported by default.
Once the XP Mode virtual PC has been shut down, select Virtual Media Manager from the File menu. Now click on Add and navigate to “C:\Program Files\Windows XP Mode”. “Select Windows XP Mode base.vhd” to add it to the media library.
Now click Add again and navigate to “C:\Users\[your username]\AppData\Local\Microsoft\Windows Virtual PC\Virtual Machines\”. Add your differencing VHD file to the media library. You should see the Windows XP Mode base vhd with the differencing Windows XP Mode vhd connected as a child, as shown. Click OK to leave the Virtual Media Manager.
Now Click the settings icon in VMLite Workstation and go to Storage. Remove any existing virtual disk attached to the XP Mode PC and add your differencing VHD file from the Virtual Media Manager.
Now start up the VMLite XP Mode virtual PC and you should find all your changes installed. If you are asked to manually sign in to the Virtual PC, the default username should be “XPMuser” and the password would be the same as used under Windows 7.
You will now need to manually install the VMLite Guest Additions by going to the Devices menu at the top of the XP Mode window and selecting “Install Guess Additions”. Follow the instructions on the screen a re-boot the Virtual PC.
(See also: Windows 8: the complete guide.)