The usb serial Palm sync cable is using and cheap and common chipset(should be pl-2303) manufacture by taiwan manufacturer, prolific, which can download from the website.
I get it work with Palm Desktop (4.2x) on OS X, but may be there is some problem with the driver, a simple data sync will take 15 to 45 minutes. The driver name under OSX is /dev/tty.usbserial.
Choose usb-serial, the option will appear once the cable plugin
This driver work well on linux kernel, module name is pl-2303.o