USB to serial convertors are notorious for problems and for slowness. Buy only the type with its own installation CD. Do not allow windows XP to install it. Manually install using CD Select COM1, or COM2, or COM3 or COM 4 port. Use device manager in your computer to check and select the right port.
Try mail order: Sadoun.com
After the conversion to serial, you will need a null modem cable to connect to your Pansat 2700E