Penguin, hey dude, sorry it sounds like you had what happened to me a while back when I was selling an old trials bike. I posted straight after I was almost done for £1500 that cheques take 10 days to "clear", and my bank made the money available after 6, stating it was "OK" after just 3! It wasn't until the 10th day when I was about to send the bike that I found out it bounced, only by luck of simply checking my balance that day!
Don't know who's sent you but it wasn't me mate.