Can the arduino plus the sparkfun USB host shield plus a decent battery be made to access one of these?
Vinculum VDRIVE2This is different from the USB host shield in that the USB protocols are implemented in on-chip firmware. Support for USB mass storage devices (including FAT32) is available. This approach removes most of the complexity and memory requirements from the Arduino. Interface is SPI or TTL serial. Hard drive size is limited by a cluster size of 512 (restricted in Vinculum firmware) to a maximum of 137GB (FAT32 will support up to 2.2 terabytes with 8kB clusters, not 15MB as Mark suggests). This would be within reach of an Arduino.
@crossroadsany idea what sort of (sustainable) write speed you're expecting?