Find out whether you actually get a second laptop delivered and, if you do, send an e-mail pointing out the error to the despatch department and then take the laptop back to the store.
When a similar thing happened to me - got two Palms delivered (on behalf of my son) rather than one - I immediately contacted the company concerned.
They were very grateful, arranged to have the second picked up and no one turned up. So I contacted them again with exactly the same result.
Then it was kept on the basis that the company had had two chances to put the mistake right and had failed to do so.
Recently I bought a set of compatible cartridges on e-Bay and two sets were delivered, although the correct price had been taken from my credit card account.
I contacted the seller who immediately offered the second set with his compliments and thanks to me for being honest - he was then going to contact the other buyer who, presumably should have had two sets...:-)