One of the basic issues of NOT backing up your data and programs...

You have reformatted and reinstalled your original operating system to "as first purchased" condition. You might be able to remove the harddrive and slave it to another computer and run some recovery programs that may or may not be able to find the COA for Office 2007. The key is not located anywhere on the CD and is usually non replaceable....although you might contact Microsoft and explain to them what you did and they may or may not discount a replacement COA for your installation CD of Office 2007.

My knowledge of this is that the COA is located on the CD case(box) or on the inside of the paper foldout that the disc comes in! You need to locate those and look for the COA sticker.