Theory Tests:
Currently (Dec 2005) only QLD and TAS require that a Full UK licence holder need to take a written test (about 30 multiple choice questions) when getting an Australian State Driving licence.
With NSW, ACT, SA, VIC and WA it is basically just a case of filling in the forms and showing them your UK licence, taking an eye test, having your photo taken (try to look good on the day you go in) and paying them.
Not sure about NT :)
In most States,
visiting drivers are not required to obtain an Australian Driver Licence providing their overseas licence is are current. A visiting driver is a person from overseas who arrives in Australia with
NO intention of becoming a permanent resident.
However: Temporary visa holders in WA can drive on a UK licence for ONLY 12 months:
http://www.dpi.wa.gov.au/licensing/m.../overseas.html
A Permanent Resident is allowed to drive for 3 months before needing an Australian Licence, after that period they would be classed as driving without a valid licence, and prosecuted accordingly. (Trust me, I was prosecuted :) )
Ignore any references to "International Driving Permits (IDP)", as these are not required for UK licence holders. They are required when your normal licence is in a different language, and must accompany your VALID National licence. An IDP is NOT a licence in itself, but effectively just a Translation of your licence.