Application Updates are generally harmless I am not sure what system update your talking about. You have a working install. Now would be a good time to backup the drive or at least your Extensions folder.

How about your video card. Check Graphics/Displays under Hardware in System Profiler. Does it say that Quartz Extreme & Core Image are supported?

If you did not check Seatbelt 10.5.5 as an option during install you may run into some kernel panics when opening disk images. Try downloading Firefox and see if you can install. (warning may require restart due to freeze)

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MOBO: Z77MX-QUO-AOS CPU: Core i7 3770K GPU: MSI N760 TF 2GD5/OC Case: Modded MacPro2,1
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