tanmc,yah that place leaves very deep and lovely memory as can seen from my nick...
i think i did also find out other route other than driving, i think there is a coach leaving Perth all the way travel to Kalbarri Seatown and near to the National Park....however in the end i give up as the timing cannot match my stay....
and furthermore there are many scenic stops along the fantastic coastal drive that you feel you will just wished to get out and stop at the cliff..so car really more recommended.
However if you still like to go by coach can try,then book a accomodation at Kalbarri seatown then there got quite a few tour agency that conduct tours to the National Park....here is the link which i gathered info from :
http://www.calm.wa.gov.au/national_parks/previous_parks_month/kalbarri.htmlhttp://www.activesafaris.com.au/12329.htmhttp://www.kalbarri.com/i have detailed driving route if you need i can send you
it is quite easy as we are also first timer at driving oversea,and just follow blindly the instruction downloaded online and managed to completethe 500km++ journey there and survive back to the airport....
and we only spend total 4 days in Perth..haaaa.a...