InstallAware

I've been using the UpgradeCode plugin (from AxoNet) for InstallAware with some success and it's exactly what I need. But I'm having problems with it on Windows 2000 Server. With the same product installed on Server 2003 and Server 2000 (with SP4), the plugin finds my old product on 2003 but not on 2000.

I'm wondering if anyone has any quick suggestions for what might be wrong? I don't know what version of Windows Installer is on the 2000 box, and I don't know how to find out. Does that even matter?

Thanks.