You need to step down the analog input voltage. Netduino's microcontroller can take inputs from 0V-3.3V.
Chris
The I/O pins on the AT91SAM7X512 are 5V-tolerant. There will not be any damage to the microcontroller from voltages up to 5V. Also, the analog voltage sources on the Gadget Shield have large series resistances thus will limit the current to safe values in all cases. No modifications to the board should be required.