I took the mic out of a Nokia 6110. It is about 5 mm diameter.
If you take the bottom off the Zaurus you can make a hole large enouigh for the mic to fit in in the top left corner above the battery. The hole does not go through to the outside, only through the inside plastic, it uses the hole on the back of the Zaurus for the sound to enter the mic. I suppose tehis bit of plastic is to lock a docking station or something, I don't know. This allows the mic to sit in the hole when you stick it to the correct place on the motherboard. (see attached pics)
The wiring can be picked up from the headphone socket but it was a long way so I traced it to the end of the red line, that shows the routing of the wire, under the SD slot and picked up an earth connection for the second microphone connection, glued the mic to the motherboard and put it back together.
The pictures are off a spare motherboard. If you need more specific then I'll have to dismantle it though I would prefer not to.