So the mouse will be connected to a micro...mmm
well, I would say you lookup the specs on of hte mouse on the net. more specifically the cable wiring.
As I understand it...mouse will have power, buttons and directions. then implement the wiring directly or indirectly (if power output is to great) to the micro.
So your C code will look or poll for signals on the micro's pins.
If this helps...good luck