HELP! Updated to 10.5.5 and my Mac won't boot

The software updates box showed up, so I merrily went along and said OK. It said that a reboot was required. I said yes to the reboot. The upgrade seemed to go along just fine. After the reboot, it gets to the grayish screen with the Apple logo on it (where the spinner should be - but isn't). It sits there for hours. I tried a power down reboot, with the same end result.

My machine is a DP G4 867MHz machine w/ 2GB of RAM. I installed Leopard clean and have done all of the Apple recommended updates.

Any suggestions? I don't relish the idea of starting over.

Thanks,
Rick

I'd boot from your install disk and see if you can archive and install - and save you losing your stuff.

Also verifying and/or repair the HD couldn't hurt to try.