People often try to cram too much into visiting australia. If melbourne and sydney are you're 2 chosen spots then there is more than enough to keep you entertained for a week in each city. That time of year will be pricey so be warned (hotels esp). As far as melbourne goes, and if its a day trip i would definately do a winery tour 1 day, maybe a trip to phillip island on another (which can be combined in 1 day with puffing billy steam train). great ocean road is good but best not to book a day tour as you will be stuck on a coach all day long. maybe hire a car and take 3 days driving down (but as mentioned this is the previous way of sydney). In sydney you'll find unlike melbourne, most of the attractions are based around the city centre but make sure you spend 2 days in the blue mountains (with an overnight stay in a cheap motel). use tripadvisor.com to work out a good hotel to stay at. great website that always helps!