After installing the Office 2007 file converter on PCs running Office 2003 some work and some don't. The error I am getting is the same as this person here. I also logged on as admin and after re-installing, it works under admin but not as user.
What Service Pack of Office 2003 are you running, and are you installing the latest Service Pack version of the Compatibility Pack?
It's a while since I've dealt with it, but I seem to remember there was an Office 2003 service pack pre-req, and that the Compatibility Pack has itself been through a service pack or two.