to insert the symbol "micro"

If I understand well what you want, try :

option key + M key (⌥ M). On my French keyboard, it returns : µ

You may get such information without us thanks to « Keyboard Viewer »

When you press a modifier key (here option), it display the characters which may be get.

Yvan KOENIG (VALLAURIS, France) samedi 21 avril 2012

iMac 21”5, i7, 2.8 GHz, 12 Gbytes, 1 Tbytes, mac OS X 10.6.8 and 10.7.3

My Box account is : http://www.box.com/s/00qnssoyeq2xvc22ra4k

Edit > Special characters > Greek > find μ > copy it

In Pages Preferences > Auto Correction > + at bottom of window to add new short cut > write a short cut > tab to next field and paste the μ > press Enter

Try it out in Pages

So did you have a French keyboard?