Have you already finished your Windows 7 product activation? If not, try that first.
Here is a MS video about activation
(It may have already been done by the company that built your computer, but if it is not yet done that might be the issue with the Office install).
My Office 2007 Standard Military Appreciation edition installed on my Windows 7 upgraded PC without a problem. Took me 3 tries to get that 25 digit key right though.