Needs to be smaller than 2g

you may need to get a micro sd with adapter. Sandisc usually work ok. But as above 2G or smaller.

When I first got my GT31 I had a hell of a job getting a 2gB SD card. I tried Office Works, camera shops and discount shops.....no one has 2gB anymore as it's so small by todays standards. I also found that "el cheapo" 2 gB SD cards don't seem to want to work, as indeed some Seabreeze/GT31 posts had suggested. I was being a tight-arse. Served me right!
I bought mine from this guy on eBay. "SanDisk" as Decrepit has suggested in his post. $7or $8 I think.
All good!!

eBay Seller information : aa774411 (41030)
New 2GB MICROSD Micro SD MEMORY TF CARD

The 1gb card that I use is working fine.

www.seabreeze.com.au/forums/Windsurfing/Gps/Where-to-get-a-GT-31

Jacko51 said.. What you are saying is as long as the card is 2GB or less it is ok. I have a 1GB card in an old camera that is not being used although not sure if it is compatible. Will give that a go until I source a 2GB card. Cheers.

1Gb is more than enough memory. My 76 sessions over 20 months are taking up 21.5mb - that's 0.021 Gb. If you or anyone get stuck, my shop (www.netplus.com.au) have 2gb SD cards in stock in Perth.

Thanks everyone. I'm really busy at the moment so I will chase it up when I catch up!