Computer does not startup after canceled software update

Question

I was installing the newest version of leopard. It seems as though leopard installs the update while the computer is starting up (?), as opposed to tiger, which downloaded the update while the computer was still on.
anyway, i was feeling impatient and decided that the update was taking to slowly and that i should just cancel it and update it later.
however i made the stupid decision of forcing my computer to turn off (by holding down the power button)
now whenever i try to turn on the computer, it will get to the screen with the apple and the rotating circle-thing below it
however, it won't get past that part, i left the computer for an hour and when i got back, it was on the same startup screen
i'd appreciate any help anyone can give me

Answer 1

You damaged your OS when you did a force-quit.
Restart your machine with your original Leopard disk in the drive while holding down the "C" key until you see the Apple.
Then you can re-install your OS. You should back up your data to an external hard drive by doing an "archive and install" which is one of the options you will have when you begin.
If you don't have a hard drive, you can just re-install the OS and then update again.
Installing with first backing up is not recommended since there is always the possibility of some problem installing new software that could result in data loss.
If you are going from Leopard 10.5 up to 10.5.2, use Apple's combo updater which should appear in Software Update.