Controlling a com port in XP with Virtual PC

I have a USB to serial adapter which will not work in WIndows & X64 because I am unable to find a driver for it.
I have set up a virtual Windows XP and I can install the USB device to give me 2 extra ports.
The software I want to use to interact with the ports is StarryNight Pro Plus but it will not run under the virtual XP mode. ( I have increased the allocated memory and screen resolution without success.)
Is there a way to run Starry Night under Windows 7 and still control a com port installed on the virtual Windows XP?
Many thanks for the help.

John