If you registered your product, you can call Microsoft at (425) 635-7056 and they will give you the installation key.
I bought a new computer and wanted to install my FrontPage 2000 on it. I had lost the CD key just like you, so it wouldn't let me install. So I called them and they gave me the key over the phone.
Although I know it's too late for you since you already formatted the HD, but under the "Help | About" menu, there is your registration number. I had that number, but not the CD key when I called them and other than verifying that I still had the original CD (by asking for the part number printed on the original CD), they only asked for my name and phone number. Since I was already registered, they had everything else in their computer already.
I'm sure if you don't have your registration number, they will be asking you many more questions.
But if you registered it, and have the original CD, then call them and ask for the CD Key. You paid for the software, so they'll be more than happy to give you the key.
