USB to Serial problem Running XP Mode in Win7

I have an old er auto cad program that run in xp. I up graded to Win7 on a new computer and run xp mode and my autocad runs well, but I don’t have a serial port for my plotter and I have one of your usb to serial adapters and have installed it on the VM xp and it is recognized as a usb to serial in my XP mode but it does not appear in my device manager as a usp to serial adapter. It shows in Win 7 device manager as I have also installed it on. Is there any way I can get some help on this matter? Thanks