Probably an easier solution would be what I did to have my Palm cradle and serial mouse hooked up at the same time to my one serial port laptop. Xircom bought Entrega and still sells their USB->Serial converter. It works really well, and will give you the benefit of getting a non propritary GPS unit, being able to upgrade your empeg from the laptop, and many other uses. Because if I remember right, the Sony GPS units use a non-standard GPS protocal, excluding you from using that new GPS with any other software or devices. Kim is working on GPS support for the empeg, and with a serial adaptor, the GPS could easially work on a Palm as well.

I recently bought the Rand McNally GPS unit for laptops for $100. It is a 9 pin serial and PS/2 device. (Power is drawn from the PS/2 port) and so far has worked very well. I plan to wire the power into the car once I get the amp and Mark II installed so that it can be used with the empeg.