Can't boot anymore (Usual solutions don't work)

After breakfast this morning I decided to do some work on the old power mac g4 of my stepmother. The files really needed some organizing (Images in the images folder, etc.) and the machine needed some maintenance. I also deleted some unneeded stuff (Norton and dmg's, etc.). And then I did something very stupid: I deleted some folders in /System/Library/StartupItems. It did still work afterwards but when I rebooted I only saw the Apple logo and a spinning wheel (Which is normal, but it didn't do anything else) When I booted in verbose mode I saw that the system said something about missing a .plist file in a folder I just had removed in /System/Library/StartupItems. Then I tried to usual things to fix it which were resetting PRAM and fsck. The normal fsck (-y) didn't work and when I tried fsck -f it said the volume was ok without fixing anything. So the only way to fix it I can think of is restoring the .plist files in StartupItems. When I held the option key during startup it did not show the os 9 startup disk so that won't work either. Can this also be fixed with booting from a mac os x install cd? Please help! (I feel sorry for my stepmother although she didn't use the g4 regularly)

Thanks in advantage.