Occured to me - an externally powered storage device can also be, for example, an MP3 player. I bought a cheap MP3 player, with an SD card rather than internal memory, and I use it for copying files to and from the SD card before using them on the GP2x. My older external card reader was taking some of the metal from the SD card contacts, so I am not using it anymore. The MP3 player is powered by an AA battery (so is externally powered). This would give a good method of external storage on the GP2x, wouldn't it?