Hello, you can download the 10.5.8 combo update, later can be bout but not downloaded.
Repair Permissions afterwords, reboot.
1058 Combo Update, 10.5.8...
Pre-Installed MacOS: X 10.4.5 (8G1453) Maximum MacOS: X 10.6.8*
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?...
Buy Snow Leopard > http://store.apple.com/us/product/MC573/mac-os-x-106-snow-leopard
Call Apple Sales...in the US: 1-800-MY-APPLE. Or Support... 1-800-275-2273