PCI Modem and com port assignment

I am trying to install a PCI Modem in a HP Vectra under Windows 98. However, everytime I try to install it, the system automatically assigns it to COM Port 4. There is no COM Port 4 and therefore, when you run a diagnostic on the Modem you get a Coul not open Port Window. I have tried installing COM Port 4, but it reinstalls the modem on COM Port 5. I have tried setting the IRQ in the BIOS. Still no luck. If you have overcome this problem before or know how to resolve it I would greatly appreciate it.