Well Blueskies...

Since i don't recommend trying to see all of Australia in two months i could suggest the following. Western Australia has lots to offer but if you want to bike anywhere interesting you'll be on the road for days...WA is HUGE

http://www.westernaustralia.com/au/P...Australia.aspx
You can ride your mtn bike along the Munda Biddi
Take your Mtn Bike over to Rottnest Island www.rottnestisland.com
Drive up the coast to Exmouth & discover the Ningaloo Reef http://www.ningalooreef.net/
Surf in Margaret River & oh yea drink wine

That's just a start...
C