If you're just trying to let the user see the difference,
another thought is to keep the Windows theme the same on both
workstations and show the screenshot from Computer A as the slide
background and show the screenshot from Computer B as a rollover
image.
This lets the user do an A/B comparison as many times as it
takes to get all the differences. You can even add callouts to the
computer B image to highlight the changed items. Assuming the two
screens are similar with the same dimensions, it can be very
effective.