On the top of this page there is a D.I.Y block that includes a brake job and there are other members who have web sites with pictures of these jobs (Thomaspin comes to mind). However, the brakes are the most important things on the car and if you are not good at wrenching or don't have a set of required tools, you should have it done by a good mechanic you can trust and who works on MB's regularly. Lets not forget we are talking 500 Aussie Dollars or about US 320. I probably have to pay that in the US too, if I have it done here.
As Kestas said, do the front first if you cannot afford both but get used to the fact that older cars are more expensive to maintain, unless you know the previous owner has already replaced all these "wear out" parts. If you don't do the work yourself, you will have to pay somebody to replace these 200,000 km old parts with new one's, which will then again last 200,000 km.