Add Com Port to Windows 98 Guest

I am trying to get an old plotter working (HI DMP-60). I have a cable that goes from the plotter to a serial to USB adaptor. I have the serial to usb adaptor installed in my Win 98 guest but I am unable to add a printer port that points to that serial to usb adaptor. If I add either a serial or parallel port to the guest it wants to save to a file. How can I add a com port that lets me point the plotter to the usb adaptor?

I am using VMWare Fusion 7.1.0 on OS X 10.10 with a Windows 98 guest.