What is using COM ports?

Is there some old Windows command or something in XP Pro that shows what is bound to COM ports?

User laptop running XP Pro having trouble with his Palm cradle serial connection, that there is no port to use. COM4 is his built in modem. He said COM3 was shown but had a little yellow “flag” next to it. He removed COM3, rebooted system still can’t get a COM port. COM1 and COM2 show in use but not what is using them. I don’t use handhelds……..anyone know how to get his cradle attached? It’s his personal laptop and Pilot he uses for work so I don’t want to tell him to buy USB cradle on his dime.

Thanks!
David