25-character product key

Recently I replaced my desktop and also wanted to reload the Microsoft Office Student and Teacher Edition 2003 software because I am taking 2 online classes. The instructor will only allow MS Word 2003 for any assignments that I am doing. I just checked out that my software and tried to load it on my new desktop, but because I didnt have the 25 character product key, I was not able to load the application. Even though I have the CD case and on the back bottom right corner is a bar code with the following numbers on the back. What am I supposed to do then?

Usually, the product key is located on the back of the Office 2003 CD case on a small yellow or orange label, where you can find it.

I checked that and there is no small yellow or any colored label out there and I dont any idea where the letter of authenticity is that I can find out. Can you tell me what else I need to do? Thanks for the reply

Can you tell us whether you bought the software with your other computer or so?