Mac OS X 10.6: If you can’t download or install an update
You may not be able to download or install an update in Software Update if you’re not connected to the Internet, the server is busy, the download is interrupted, or your Internet connection is too slow.
To successfully download or install an update, try the following:
Choose Apple menu > Software Update. If a message appears that says you’re not connected to the Internet, check your Network preferences.
When Apple first makes updates available, the server may be busy for a while. Wait a few hours, then try downloading the update you want.
Turn off your screen saver in the Desktop & Screen Saver pane of System Preferences, and set your computer not to go to sleep in Energy Saver preferences, so the download and installation won’t be interrupted.
If your Internet connection is slow, try downloading the updates and installing them later.
If your computer is managed by a network administrator and you’re experiencing problems with Software Update, contact the administrator.