A POA is usually a separate piece of paper to a will allowing other people to make decisions on a person's behalf.  We went through this with my Dad.  Thing is, if you don't already have one, it might be difficult to get a lawyer to sign one, because your Dad might not be judged as competent to sign a POA.  

http://www.act.gov.au/browse/topics/law-and-justice/wills-estate-planning-and-power-of-attorney

That's for the ACT, but there are links to information on other states.