I'm not going to tackle the 2nd part of your question, as any number of the questions tagged with international-transfer should cover you on that. There's no way to transfer an ISA into an Australian tax-free savings account, so no need to worry about anything special there. Don't forget that the FX rates change quite a bit over time, and different methods have varying fees, so moving at the wrong time could easily cost you more than the missed interest!
For the first part, it depends. One thing you should seriously consider right away is switching your ISA money into one paying a better rate. Check the best-buy tables online or in a paper, as you can get a lot better than 0.1% on a transfer in, even with current depressed rates. At least that way you'll earn more interest while you decide.
As for when to transfer, that's something you'll have to calculate for yourself, based on your marginal tax rate, and your view of how the FX rates will shift. If you're a 40% taxpayer, then 2% in an ISA is worth the same to you as 3.3% gross. Don't forget to consider both your UK and Australian tax rates in the year you move, as most likely you'll have to pay the higher of the two. The westpac rate looks like you might struggle to beat a decent ISA over the course of a year, were you a higher rate tax payer. Oh, and don't forget that you'll likely loose the tax-free status of your ISA once you're an Australian tax resident, so you'll need to start paying tax on interest earnt in the ISA once you're out there.