HELP How to rescue data from a HD with only the Terminal utility working

I can no longer access the hard disk on a 2008 unibody Mac Book after an failed OS upgrade (?). Running the original OS 10.5.5 from the grey CD-ROM that came with the device and using the "Terminal" utility, I find all data in their place and within the correct structure.

I tried to make an image of the HD or to copy the files to the external disc using the Hard Disk utility, but all attempts have produced an "operation not possible" message. Target mode will not work, as the device has no firewire connection implemented.

How can I access the files (I know they are there, I can see them...) and e. g. copy them to an external disc or rescue them with an other method?

PLEASE HELP ME

Thank you, Martin

PS Please don't tell me that experienced users will always have backups of their files: It is my wife's device and that's exactly what I have been telling her for years. Still, it's my wife...