Cleaning OSX on Mac Air before Sale

Hi
I have an early Macbook Air v1.1 13.3 64SSD and am selling it to buy a new one

It was a very early one which had Leopard (original DVD), which I upgraded last month to Snow Leopard (via DVD) and then to Lion (Web install).

When I come to sell it how can I reset the OSX to the original (ideally Lion) so that none of my data is present and the new owner can start from scratch.

I don't really want to reset to Leopard.

FYI I am buying the same 13.3 Air but with all the new goodies; i5, 128SSD, 4GB, card reader and longer battery.

From a PC background i am really enjoying using the Mac though!!

Thanks,
John.

To get a clean install of Lion, you'll want to grab a copy of the installer again from the MAS and then put it onto a Flash drive or DVD using the instructions here: How to burn a Lion boot disc | TUAW - The Unofficial Apple Weblog

Now, boot up your Macbook Air with the Lion install media and erase the HD and re-install. Once finished with the install and then Lion tries to reboot, turn the computer off. This way when the new owner turns it on, they should get the entire welcome video and allow them to set it up like a new Mac..