HK has a fast train to the central metro station downtown and a collection of airbuses that go more slowly but will drop you at your hotel - except the one I caught this month, which dropped me a mile away, the clot.
Have a look at the links here
http://www.hongkongairport.com/eng/index.html
I haven't been to Tullamarine for ages but this is their website
http://www.melair.com.au/to_from_airport/
Sorry I don't know the Langhams specifically but they may well offer their own transport.