Far From Oz,
The 4 months full time quoted to you by the flying school was about right.
For a PPL you are looking at upwards of 50 hours training, take into consideration bad weather and aircraft/instructor problems and three weeks is looking too short.
If you set your sights a little lower it wouldn't be impossible to obtain a GFPT (the restricted licence Ozexpat was refering to).
There is no substitute for experience and you gain very little in 3 weeks. I'm biased but I'd say there is a big difference in the skills of an Australian trained pilot to that of a pilot trained in the USA.
If you've only got 3 weeks, learn the basics in Oz and maybe finish your PPL training in the UK at weekends??? Background study before you even get near an aircraft will help you greatly.
Good Luck!
