None of the Rabbit products support USB devices for storage.
Some of the 3000 and 4000 products include SD card slots.
The 3000-based products are currently limited to SD cards only and don't support SDHC (2GB to 32GB cards).
The 4000 and later products (RCM4300 series and adding an SD slot to any 4000/5000/6000-based module) have SDHC support as of Dynamic C 10.72C (released soon).
SD/SDHC cards limited to using 1 to 4 FAT16 partitions of 2GB or less.