Windows Media Player won't see my Windows Mobile 2003 phone

I have two PCs, one with Vista Enterprise and one with Vista Ultimate. Both
have WMDC installed and both have the hotfix described in KB931621. However,
only the PC with Vista Enterprise seems to fully work with the phone. I have
tried this with both an Orange SPV c550 and an Orange M3100 and neither
devices will be recognised by WMP11 on the Vista Ultimate PC.

Been through all sorts of troubleshooting including dissabling the firewall
but get nowhere. I can explore the devices and their storage cards but that's
all. Would love to be able to sync with WMP11 and Napster.

Any thoughts??