Electronic charting without a serial port...
You need to purchase a USB - Serial adaptor. In Canada there is a product for sale at Futureshop that does this. It is called "Belkin Serial to USB Adapter" and is $49.99 Cdn.
It is also available from their web site and has web id 10010579. Their site is www.futureshop.ca
You might also try your laptop manufacturer web site. They likely sell such an adaptor or a docking station for your laptop.
Best of luck