Here's what I did:
I installed Ubuntu Desktop 12.04 onto the workstation, and set it to where the user automatically logs in (an option during installation).
Then I installed Virtual Box:
sudo apt-get install virtualbox-ose
Then, I installed Windows XP into a VirtualBox virtual-machine.
After that, I launched virtual box and right clicked on that virtual machine and selected "Create Shortcut on Desktop".
With the shortcut on the desktop, right-click on it an go to properties. Copy the command that launches this specific virtual machine.
Last, from the power menu of Ubuntu 12.04 (top-right), select "Start Up"; add an entry named Windows XP and paste the launch-command you copied from the Desktop shortcut you created. Alter that command by putting in the --fullscreen parameter.
After you do all this, you can reboot the workstation. It will automatically boot and log into Ubuntu, then it will automatically launch the Windows XP virtual machine fullscreen.
The employee doesn't have to know anything about ubuntu. The only thing you have to tell him, is that instead of ctrl-alt-delete, he must hit right-crtl-delete to get to his windows login prompt.
Before you let the employee use this virtual workstation, you'll want to clone it, and save a copy of it elsewhere (so if he ever screws it up, you can use replace his virtual machine image with the one you initially created).
To move this 13gig file somewhere else, I installed openssh-server onto the ubuntu workstation:
sudo apt-get install openssh-server
After this, from the destination machine I installed filezilla client:
With Filezilla, I was able to login to the ubuntu workstation via sftp, and download the cloned virtual machine for safe keeping.