Possible Duplicates:
Is it possible (yet) to use old laptop TFTs as extra monitors?
Can I use my laptop as a second monitor for my desk computer?
I've an old 15" XP laptop, it's just lying around as it's useless in this day and age (How useless? Try a 400MHz CPU, 128MB RAM, and a 3GB HDD).
I just saw this post about the exact same topic, but that thread is regarding Linux. I'm running Windows.