You have probably seen so-called Nigerian scam e-mails sent by purportedly rich persons, who need to discreetly move money to bank accounts in US, UK or other countries abroad. They ask you to help them by using your bank account in exchange for a large share of a sum that needs to be transferred. Scammers might also send you “official” documents and other real looking stuff. Then they usually ask you to give them a loan (thousands of dollars or even more), so that they could bribe someone in a bank in order to move a big sum to your account.
Of course, you don't get your share, and scammers simply steal your money. That's how the scam works. But no one falls for it today. That's why criminals decided to introduce a new form of Nigerian scam.
Now you receive a letter not from a stranger in Nigeria, but from an American soldier in Iraq. “The soldier” writes that he has found a treasure, a lot of gold or diamonds, and needs to move money home. However, he cannot do this alone, so he asks you for help. Just like in a classic scam, you have to give him money he needs in exchange for a share of found wealth. Needless to say, that you won't be paid. You just loose your money.
Why criminals are using a story involving an American soldier? The answer is simple. New form of Nigerian scam is targeting primarily Americans. They won't believe a Nigerian, but some of them might trust US soldier, especially if a letter is written in good English, and “a soldier” is seriously injured. A lot of people would try to do something to help a fellow American.
Even if you are an American and a great patriot, DO NOT fall for this scam! Sending your money to someone you don't know is foolish.
More details can be found in the May State of Spam report by Symantec.