Hi Luca
If your using the 2.4Ghz Series 2 Xbee modules (p/n XBP24-B???-004) then these wont work on the DIYDrones XtreameBee Board. The Series 1 XBee modules (p/n XBP24-A??-001) work fine. The cheapest solution is to get the Sparkfun Regulated Explorer Board, or XBee Sheild, Both Series 1 and Series 2 Modules work with both of these.
Best Regards
Sam