I have my visa for Australia (achieved in dec 09). Do you mean the medical for the visa?
If so you all have to have a chest Xray, blood tests plus a test to check for HIV plus another test to check for Hep B and C and a medical by a registered GP (only certain Gps are allowed and you get a list in your area, same with the Xray dept who does your chest Xray- only certain ones are validated). So you cant really do any of these early. You have to sit and wait for them to be requested. Our agents sent the forms to us early so you can fill those in (but doesnt take that long anyway).
Hope that helps