OS X won't boot after system update

Hello,

My mac just downloaded the latest 10.4 system updates (over 100megs) and after installing them told me to reboot, which I did.
Now I can't boot my system anylonger. I get the chime and then the gray screen with the apple in the middle and the turning wheel at the bottom. Single user mode works, but I can't boot in safe mode.
I tried all the Mac os X troubleshooting tips above, disconnected everything from my mac except mouse and keyboard.
I also tried all of these:
http://docs.info.apple.com/article.html?artnum=106464
Nothing seems to work.
fsck tells me the volume is ok.

Any ideas, similar problems,...?

Thanks,
Vincent

A little more information is needed.

What version of 10.4 were you running before the upgrade?
What version of the upgrade did you download?
Was it the combo update?
Are you updating you G4 PowerMac or some other system?

I don't update the OS any more, as after I do some software won't work, new tasks have to be learned and no speed increase results.

Just looked at you link above, that is for 10.3.9 and earlier.