eh i dont think so because the windows install thats on your current hdd has the hardware configuration of the one its in right now. it would only work if you moved it to another pc with the exact hardware.
you could get the windows 7 rc for free which will last you until i think june of 2010, at which time you'll have to purchase it.
if you are gonna use 7 you can either backup your data and do a new install or dual boot.