I cannot make any comment as we do not know anything about OBDII but I find this on their web site on cables to use:
Dell Axim X50/X51:
http://www.pc-mobile.net/ax50.htm See part number PX50GP. Note: this adapter must be powered using a 12V car power adapter, available separately. A F-F null modem cable is required to connect to an MQ200. The MQGPS RS-232 plugs in directly. These cables are also available through the MaxQData custom order pages.