Office proplus error on install

[Aspie]

When I try to install Office 2003 I get this error message

The feature you are trying to use is on a network rsource
that is unavailable.

Click OK to try again, or enter an alternate path to a
folder containing the installation package 'PROPLUS.MSI'
in the box below.

I click cancel and it installs ok, but I can't install
the service packs for Office now as when I try it throws
up the same error. Where do I fond the file proplus.msi?

Thanks