This sounds like a question to ask of your computer vendor, since there's no
specific place a vendor has to place distribution kits.  They can put it
where they want, as long as they supply you one.

However, if Office was installed using that on-disk distribution kit, the
installation script should remember where it is and go back to that same
place when you attempt to install the Excel exporter.  It can't hurt to give
a try to installing it.  The wort that will happen is that you'll have to
cancel the install.  It won't hurt what's already there.