That's exactly what I needed, thanks!
I managed to get the coolant expansion tank replaced last night. So I at least managed to get to work this morning. I did however still recieve the 3F fault code, indicating a problem with the thermostat. The hose leading from the thermostat towards the expansion tank was hot, however on the other side it remained cold. I'm not sure if that indicates that it is stuck open or closed, however, it's stuck somehow... I won't be able to try this procedure until I get paid on thursday and make it down to Daniels or Jeff's to pick up some BMW coolant. I'm only going to use the car for absolutley nessacary trips until then and keep the heat on full blast to try and avoid overheating.
Thanks again though, I'll make sure I bookmark that page. It looks like it has some very very useful information.