I have found that one way to access the extremely attractive listing fees and fantastic incentives (that more than compensate for FVF that are levied on post) offered to US sellers on the US site is to register an id via ebay.com - and go through the prompts accordingly. 

In any case, my advice is to log onto ebay.com and have a good read through the policies that apply to the US site, as buyer and seller disputes are managed quite differently, you must offer post to the US and there may be some $$$ involved in the US to AU conversion rate when you make payment of your US ebay seller account.