In the words of the form email provided:
"As an Australian I believe that I have the right to express myself in my own variety of English."
Aussie, Aussie, Aussie, Oi, Oi, Oi!
P.S - Don't let the need for an email address put you off. What? You don't believe Microsoft already know your email address? Use your secondary address, or if you don't have one, get one.
Email your support here ... scroll down the page.
First handy-dandy fact: if you hang about with the page open for too long (say, ten minutes), before eventually get around to remembering to fill in the blanks and hit the submit button, you get thrown out to the logon page because the petition page has timed out. Cure: start again, refresh the page.
Second handy-dandy fact: following my written inquiry, Macquarie kindly provided the following, by way of explanation for the petition, seeing as MS Word 7 ostensibly does have an Aussie spellcheck option (as helpfully evidenced in the comments by Aussie ex-patriot Dylan):
"Regarding the Spellchecker, yes Word comes with an Australian English option. It has, for many years, come with this option but it was Microsoft's version of Australian English which wasn't particularly Australian (for example, it would accept 'realize', with a 'z', as correct). So we produced the Macquarie wordlist and to do this we required Microsoft to give us the software that could produce the correct files specific to Microsoft Word's spell checking system. In recent years Microsoft has upgraded Word and changed the spell checking system but has not given us the updated software to produce the spell checking files in the new format. To produce a Macquarie spell checking wordlist for Word we need Microsoft to give us the right software OR to include our wordlist as the default Australian English. It's obviously a commercial decision for Microsoft (and Apple) to include external data in their software products and one way to influence those sorts of decisions is with consumer pressure. We already received lots of requests for an updated spell checker so we though we'd make the most of that. Hence the petition."So, there you have it!