Perth is great, but if I had a week I would head to Tasmania, no question. With a rental car you can easily do a circle trip around the island, hitting Hobart area, Freycinet, Launceston, Cradle Mountain, Strahan. Wonderful outdoor scenery, walking/hiking, with a lot of variety. Quiet and laid back, with a bit more sophistication in Hobart, but unless you want nightlife, Tassie is the place. I last did this in March 2006 and can't wait to go back.

Flying in and/or out of Launceston offers additional flight options.

Enjoy your trip to Australia - my favorite place to visit!