It is not the software, it is the bootloader that restricts what size card can be used. Using the latest bootloader will allow use of up to 16gig SD card. The POI can only be kept in the map folder. They cannot be stored separately on the SD card.
i can t tell you the specific format but i ordered two 4gb SD cards from USA, they looked cheap but the tomtom 710 uses it . All of the 4GB can be seen and accessed. I have USA, Canada, UK Europe all on it! it works great! I can tell you that I cant find another that works with it( BTW! its not SDHC!)!