Microsoft Office Enterprise 2007

I recently purchased a new computer with Windows Vista Home Premium 64-bit. I took out the hard-drive on my old computer, which was running Windows XP Professional, and put it in my new computer. While attempting to reinstall Microsoft Office, I was prompted for a 25 digit product key. Now I purchased this software over the internet from an old email account which I no longer use, so the confirmation email I received with my product no longer exists. I'm wondering is there any way I can find the product key for Microsoft Office on my old hard drive? I already tried using regedit, but it cannot run off my old hard drive in Windows Vista. Any help would be greatly appreciated. Thank You.