This device looks like it probably uses the serial sync cable to move data in host mode.
Although you can't directly access USB data on an external device (e.g. play MP3's from an external hard drive), I've seen Compact Flash adapters that support USB OTG. This means that you would be able to copy data from a USB hard drive TO your pocket PC, but you wouldn't be able to directly access the data on the hard drive, due to limitations on the protocol.
However, you don't have a Compact Flash slot on your device. So, there's really no way for you to get USB to work on that device. The adapters are pretty expensive & hard to find, anyway.