Saving off Windows to install Ubuntu

[John R. Sowden]

I have 6-12 windows computers that I am not using because the windows os 
is part of what gives value to the box, as far as most of the buying 
world views it.

I would like to (a) get rid of any non-ms programs and any data from a 
computer and then save the ms windows "image" to a dvd, mark it as 
associated with that specific computer,
the wipe and install ubuntu.

Then if I ever wanter to sell the box, I could remove ubuntu and install 
the specific windows for that computer, and sell it to someone as a 
working ms windows computer.

How do I reliably do this?  Do others have the same issue?  Laptops are 
even worse due to windows required hardware.

John R.. Sowden