HAHAHA, my Intuous3 came with different kind of nibs. They're made of different materials, and one of them is spring loaded, I'm just curious about how they feel, perhaps I will like one of them better.
Here is the exact instructions from the Wacom site itself..
"Take a tweezers and pull the plastic nib out of the top of the pen. Insert the new nib and tap the pen down lightly to ensure it is in place. Do not try to open the pen under any circumstances, since This will only damage it."