I would pick up another fan like this one in the link below (make sure it's for a chipset, i.e. a northbridge/southbridge)
Then take out the motherboard, and if you turn it over you can see the plastic plugs on the opposite side from the broken fan. Clip those pieces of plastic to get it off. Clean off any thermal compound on there, then reapply some new thermal compound, and install the new heatsink/fan.
I did it a while back with on of my boards which had a chipset cooler fan die (it was really loud). It was pretty simple and fixed my problem.