Can't Install Office 2007 Small Biz edition on new pc

Hello,

My old computer, running WinXP died. I have a new pc running Windows 7. My
problem is that I originally had Office 2003 installed on my old pc and
upgraded to Office 2007. I can no longer find the original Office 2003 CD. I
need to install 2007 on my new machine. I had registered 2007 with Microsoft
on my old machine but I understand that you can't install an upgrade edition
without having a full copy of the software you're upgrading from already
installed. Since I can't find the original Office 2003 CD, I need to know how
I can install the Office 2007 upgrade edition without having to re-purchase a
full copy. Thanks for your help.