Hmmm, have you applied the big 10.5.8 update?
Repair Permissions afterwords, reboot.
1058 Combo Update, 10.5.8...
Do Finder windows open?
In Finder see this folder...
Does it contain...
Does this file exist?
When I first re-installed it was with the option to erase the disk.
I'm unable to update the software other than with the link posted above as the machine is not connected to the net; I downloaded the above onto my laptop and moved over.
I have a wireless USB installed but cant go through System Preferences or the Wireless Utility (which doesn't open either...)
It could be a strange hardware fault but it may be best to try and install again from the DVD.
Select Disk Utility from the top menu after language selection and erase the disk.
Do not attempt to import anything during the install process.
Download the combo update direct from the internet as soon as you have it connected.