As described in http://www.gumstix.net/Setup-and-Programming/view/Overo-Setup-and-Programming/Cabling-and-Compatible-USB-devices/111.html it tells me to use the USB OTG with mini-a to mini-b cable.

To use the USB OTG port of an expansion board of the Overo series in host mode you must use either:

Thanks, 
 
Marcus