If I were to take Lion off of my 2008 Macbook Pro by reseting it to factory defaults, and if I were to want it back, would I have to pay for the OS again?

I've got an early 2008 Macbook Pro, which I believe initially came with Leopard. I put Lion on it last year, but now I need to partition my hard drive with Windows XP, and to my knowledge, there is no way to partition anything but Windows 7 when using BootCamp.

I don't love Lion, it's OK. I could sleep at night if I parted with it.

If I ever wanted it back, could I download it without having to buy it again since I've bought it once already?