A bit of info to add to the archives for the 5x00 serial port...
First, the most frustrating part of making my own cable was finding an authority on just which side of the connector pin 1 was located. For the record, pin 1 is located on the LEFT side of the zaurus. Pin 16 is adjacent to the power connector.
For quick reference - Pin 3 on the 5x00 is Rx, pin 4 is Tx, and pin 8 is ground.
Rx activity on the serial port can be viewed from the command line:
> stty -F /dev/ttyS0 xxxx (where xxxx is the baud rate, such as 9600)
> cat /dev/ttyS0
This site has the most complete info I've found of user-contributed tidbits. Included are pinouts for serial cables in both DTE and DCE flavors, info on the DigiTraveler, and NexTel phone connections.
Serial port connectors can be purchased from http://www.fivestarassoc.com/Z/
They also sell some pre-assembled cables for various functions. The connectors supplied are low-profile and do not interfere with the keyboard opening up. This company is also working on the design of a break-out box.