If you are an eligible U.S. voter living overseas, the Democratic Party offers the option of voting in the Democrats Abroad Presidential Primary instead of voting in your home state primary or caucus. The Democratic Party will seat Democrats Abroad voting delegates at the party convention, so it is a real primary.
There are certain rules you must follow, including especially that you can only vote in the Democrats Abroad primary or in your home state primary, not both. Also, you must be a registered member of Democrats Abroad by January 31, 2008, in order to vote by fax, Internet, or mail. Details are here, and you can register here. It's quick and painless. Otherwise, you'll have to vote in person in certain cities abroad, and you can also register in person if necessary. The primary will be held from February 5-12, 2008.
There is a Republicans Abroad organization, but as far as I know the Republican Party does not hold a global presidential primary for U.S. voters living overseas. If you wish to vote in a Republican primary or caucus, you'll have to do that through your home state. If it's a caucus or convention, you'll have to travel back to your home state to participate in person. Note also that you cannot be both a Republican and a Democrat in the same election cycle for purposes of voting for presidential nominees. For example, if you vote in your home state Republican primary you cannot vote in the Democrats Abroad global primary.
