If you have another mac with firewire, you can also try booting it into target disk mode and running disk utility on the other mac.

One thing to try if you get a boot-able OSX install cd /dvd is -- before re-installation of os, selecting disk utility from the menu and running "repair disk" on hard drive. I've corrected this kind of problem before (and even the question mark folder symptom). This will prevent loss of files on the disk.

One last reminder, make sure the OS install matches the drive. Some TI books did not come with DVD so if you get a Tiger install DVD then your back to using the TDM method.

JHV