The currency of a listing is determined by the site that it's listed on, so to be able to have listings in USD, you need to list on eBay.com. I don't know all of the sites that use Euro - Ireland, Germany and France do, but I don't know any others off-hand. To list on these sites, you can either log into them using your normal login details, or go to your site preferences and change the setting that allows you to send listings to multiple sites while logged into eBay AU. (Under selling manager pro, there will be an option that says "list on these worldwide eBay sites", default is set to Australia only, if you click edit you can add additional sites). Just be aware listings on these sites need to meet the respective policies for each one, you can also list the same item on multiple sites, but I wouldn't recommend making more available this way than you can supply, just in case you get orders you're not able to fulfil.
Not sure if you meant you've already set up your PayPal account to receive and hold balances in other currencies (if you get paid in a foreign currency and don't have it set up to hold a balance in that currency, it usually just automatically gets converted to your default currency), but if not, you can log in to your account and click the currencies link on the left, the next page will give you an option to add currencies and you'll be able to hold balances in those selected without them being automatically converted.
PS the currency conversion fee is always charged by PayPal, but who pays it is determined by who they do the conversion for. If the conversion is done at point of purchase, buyer pays it, if it's done after you receive it, you pay it, so that's something to take into consideration.
