I cannot speak to your exact situation, but one that is perhaps similar.

We have an excel  2003 workbook  full of macros and NO links to the outside
world. We publish it in MOSS 2007, and want our corporate users to be able to
open it and exercise its macros. If the user has a pure Office 2003 or pure
Office 2007 setup, it works fine. However, some of our users have a PC with
Office 2003 BUT with some 2007 components installed. This crashes & burns the
IE browser.