Ride lots
This question maybe should go in the "form and fitness" section, but anyway... For an event like this, the preparation is all about riding as much as you can fit in, mostly at a fairly low intensity.
In a nutshell, you should should be doing long rides, mostly at
E1, and learning to spin - that is, pedal at a high cadence of 90-100 rpm. Perhaps you should throw in some hill work at higher intensities, but mostly it's just riding at a comfortable pace.
Obviously, if there are hills - and seeing it's Tasmania, I can't see how you can avoid them - if you could lose a few kilos, you'll find things so much easier.
It's also really important to get your equipment sorted as far in advance as possible. At a basic level, is your bike fit, including saddle, gloves, bibs (you are wearing bibs, aren't you?) comfortable over multi-hour rides? Have you found a saddle that works for you? Have you used saddle cream? Do you have an energy drink that agrees with your stomach? And what about food? Are your pedal cleats in the right position? Trust me, multi-day rides like these will find you out on comfort issues in a way that one-day events don't. I've never done a week-long formal ride, but I did 3 days covering the route of the 2009 Tour through the Pyrenees. By the end of it I had nasty saddle sores from a badly fitting saddle. I made it through the 3 days - just - but it was clear to me that I wouldn't have been able to ride much further.
Good luck and have fun!
I have never done anything more than 1 day races and was hoping to get some advise regarding training for this week. 
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