No software will update

[MacHelpPlease]

Hello,
I have a mac os x version 10.5.4 and its been working fine for ages. ive had it a few years now and had no trouble.
The problem i'm facing now is that every time i try to install new software from the software update program, the updates fail to install. I have tried to install the new version of itunes (9.2) and the newer versions of mac like 10.5.8 and these updates always fail.
The error usually says 'run preflight script for itunes' etc. depending on the update im trying to install
I have never seen this before and i have no idea how to fix it. So any help would be appreciated. thanks

 

[GGJstudios]

Try repairing permissions.

 

[MacHelpPlease]

Ah i tried that and that gives me error messages saying:
The underlying task reported failure on exit.

Thank you for the help though

 

[GGJstudios]

Ah i tried that and that gives me error messages saying:
The underlying task reported failure on exit.

Thank you for the help though

Did you try Repair Disk from Disk Utility?

Disk Utility reports "Underlying task reported failure" when repairing a volume

 

[MacHelpPlease]

Did you try Repair Disk from Disk Utility?

Disk Utility reports "Underlying task reported failure" when repairing a volume

Yeh i did that. Thanks ill have a read through and see what i can do. bit worried now - looks like it might a serious problem :\