I have given a good explanation of the process here:
http://aurora2.pentarch.org/index.php?topic=11545.msg144977#msg144977My guesses are:
1- you haven't got many on the surface and progress are proceeding slowly (you can check by saving, put like 100 units on the surface by SM and skip time 30 days and see if you have updates)
2- you haven't created a colony on planet before dropping the units (if so just pack all the units back, cancel the colony and create a new one)
3- you are experiencing one of the many refreshing bugs. (If you save, exit, and reload you will most likely fix it)
My dollar is on number 1 though.
EDIT: If you not receiving updates on the event screen does not mean the people are not "working" on it.