Read thru here to learn about it. It's called "scambaiting."
http://www.419eater.com/and
http://www.potifos.com/fraud/
Like I said earlier, a friend of mine bought an XBox 360 and tried to sell it on ebay to make some good money (which he did, BTW). The winning bidder sent my friend an email saying he's from Va..lives in England..but his daughter is in Nigeria. He will send his payment as soon as he gets comfirmation the package is on it's way. So basically, he was going to get the XBox shipped to him w/o paying.
Don't EVER send anything until you are 100% sure you've been paid. If you receive a personal check as payment, it will take up to 6 weeks to clear. If you deposite the personal check, then send out the package...the check can bounce...so the bank takes that money out of your account..and you've already shipped the package...so you're screwed both ways.