I'm not sure if i am posting this tread in the right place, but hopefully I am. My Macbook Air late 2008 running os x 10.5.5 won't update to 10.5.8 using software update. I downloaded the update no problem with software update, but when I try to restart the computer so the update will install, it will ask to install the updates, and I chose the option to install them. During the process of instalation it will say: "The update 'Mac OS X update Combined' can't be Installed The installer could not validate the contents of the 'MacOSXUpdCombo10.5.8' package. Contact the software manufacturer for assistance." and then the only option there is is to restart. I hope someone can help, Thanks!