You must get a 10.6 Install Disc.
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.
Which apps work with Mac OS X 10.6?...
It looks like they might still have it...
If it's a core Duo & not a Core2Duo, then it'll only run in 32 bit mode.
If your a MobileMe user I think Apple has a free Disc available.