PJ they have a utility called NAVilink, download from their web or on the CD that came with your 31, it's been many moons since I have used NL so no how too's from me. You can save your data to card and then get it that way, much easier.

I believe the biggest card is 2GB, copy and pasted below Benny can help Oh and formate the card via the 31 a couple of times before use.

GT-31 provides power of 2.8VDC.

The following cards have been tested to work with GT-31:
SanDisk 2GB
Transcend 1GB
Kingston 2GB
PNY 2GB
Apacer 2GB 60X

Compatible/Suggested SD card to go with Locosys GT-31/BGT-31 or SD cards (<=2GB) with 2.8VDC(3.3VDC~2.7VDC) power input should work.

Wish I was faster than you on the water Mike

Cheers lads, I ended up pulling an old card out of something that seems to work after spending ages trying to muck around just with the cable.
To easy.