I want to add that I've heard of these things happening before, so don't be so quick to judge the OP.
Quite a few people are victims of this kind of scam. I mean, if people never fell for it, this type of scam wouldn't even exist. The moral of the story is don't send money orders to people you meet on the internet, ever. Face to face is much, much, MUCH safer. Oh, and don't shop on Armslist.