Hi, by download, do you really mean you tried to install it from a DVD?
Where exactly are you seeing this needs 10.5 at?
Even the oldest 2007 MacBook can run 10.6...
Snow Leopard/10.6.x Requirements...
* Mac computer with an Intel processor
* 1GB of memory (I say 4GB at least, more if you can afford it)
* 5GB of available disk space (I say 30GB at least)
* DVD drive for installation
* Some features require a compatible Internet service provider; fees may apply.
* Some features require Apple’s MobileMe service; fees and terms apply.
You will have to look on eBay or Amazon fo a vlack retail Leopard install disk. It may cost up to $200.
The OS 10.6 Snow Leopard install DVD is available for $19.99 from the Apple Store: