Sorry to say, you're out of luck with 10.5.8, Apple only released it for 64 bit IntelMacs using 10.6.x & up...
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?...
Call Apple Sales...in the US: 1-800-MY-APPLE. Or Support... 1-800-275-2273