Extract MS Office 2008 Key

I have googled this, and found questionable results and software.

I have decided to upgrade my OS X 10.5.8. But I would like to start with a clean install and then upgrade to 10.6 and then as far as Maverick.

The problem I have is that, I have a legitimate purchase of Office 2008. I would like to keep my office, but i no longer have the original (if i came with one), DVD. How do i retrieve my Office Key so that I may reinstall it once I reinstall OSX and update it?

Thank you for any help.