Cannot update any system software

Question

I currently cannot update any system/apple software in any way.
If I run Software Update from the apple menu/system prefs, it informs me that my software is up to date, even though this is clearly not the case.
If I download the updates manually from Apple's website, they refuse to install. When I get to the Destination selection screen (i.e. "Select a Destination: <list of volumes>"), my startup disk is disabled! In the Installer log it says the following:
=== Starting check on volume /
Requirement: requires "certain file content criteria" PASS for root=/, domain=0
Requirement: requires "certain InstallationCheck criteria" PASS for root=/, domain=0
Requirement: requires "certain VolumeCheck criteria" FAIL for root=/, domain=0
=== Starting check on volume /
Requirement: requires "certain file content criteria" PASS for root=/, domain=0
_volumeAppeared: volumeCheckTool disabled Ti (this is the startup volume's name)
This first happened to me when I tried installing the QT 7.1 and Security Update 2006-003 updates back in May. It's still happening now with iTunes 6.0.5 and QT 7.1.2. The last thing I installed through SU was Security Update 2006-002 back in March.
Any ideas? This really, really *****.
PowerBook G4 867 mHz Mac OS X (10.3.9) 512 MB RAM, FireLite 80GB FW disk
PowerBook G4 867 mHz Mac OS X (10.3.9) 512 MB RAM, FireLite 80GB FW disk

Answer 1

hm, you used to be able to edit your own posts. not anymore i guess.
the thing i want to add is that i have repaired both my permissions and the disk itself on the startup volume, to no avail. neither console.log nor system.log say anything when Installer fails on its volume checks.