You need to have a credit card with a billing address in the United States. If you have that, I think you can use the US Store in another country, just select United States in the drop down menu at the bottom of the page.
Josh's call from Epiosode 313 got me thinking. Well let me just say straight off the bat I am a dual citizen of Australia and the United States of America by birth. I currently live in Australia and can confirm that the Aussie iTunes Store sucks. So I am American citizen and I want to hand Apple money. Why cann't they just take my money and give me content? Just grrr
Is it possible to proxy iTunes or what not?