The best way to get from Melbourne airport (Tullamarine) to the city is to catch the Skybus. It's a lot cheaper than catching a taxi (which is the only other way to get into the city besides hiring a car - I guess this could work out cheaper though if there's a few of you) and leaves roughly every 10min, and it will drop you right in the middle of the CBD, or in some cases right outside your accomodation. Costs about $15 one way per person I think.

If wanting to travel from Victoria to Tasmania (or vice-versa), you can take the Spirit of Tasmania ship (as long as you don't get sea-sick!). This journey is overnight and has great ocean views.

Conveniently located close to Melbourne City Centre with plenty of safe public transport.

Tram straight up from Collins street - 109 or 24

To get from the airport to the city, take the Skybus. It has a regular service to the Southern Cross (formerly Spencer Street) railway station. From where the hotel shuttles take you to your destination. The sguttle is included in the ticket price. Tickets can now be booked printed in advance on the Internet with your credit card. A return gives the best value. The TV on-board runs visitor info, which is handy if you haven't been before.
http://www.skybus.com.au/