Just to clarify, there are two "parts" of the Windows product - there is the Windows CD/DVD and the activity code.
The Windows CD/DVD on its own, without the activity code, is worth nothing so they are available to download from the internet.
The activity code is the thing that costs the money, so the one on your laptop is unique to you.
All the images of the Windows CDs/DVDs are on the internet on a website called DigitalRiver (but I am not sure for how long).
So you can download a Windows CD/DVD from there.
Here is a forum update that explains it all
http://answers.microsoft.com/en-us/windows/forum/windows_7-windows_install/digital-river/66a8439b-0d16-4b70-92f7-1c8486a46ebf