recent updates have killed my system

I have an iMac 2.8 GHz machine with OSX version 10.5.8.

My daughter wanted to update her itouch to the latest version of iOS today but before I did, I was prompted for some updates to OSX.

The updates were:

iWork Update 4 v 9.0.4
Security Update 2010-005
iTunes v10

I downloaded the updates, rebooted and brought up iTunes to download iOS v4.0.2.

Everything seemed fine and the iTouch update was downloaded but then seemed to get stuck on extraction.

I rebooted the system (power cycled - the system was locked) and then proceeded to have problems with system performance.

I rebooted in verbose mode and didn't see anything out of the ordinary.

I then rebooted with the install disk and ran a disk check. That reported no problems.

Unfortunately, the system seems to be totally screwed. It will lock up at random times and switching between applications is unbelievably painful.

Is it possible to uninstall these updates? Can I get rid of them one at a time to see which one it was? What other possible things could it be?

I really need some help debugging this one. I'd rather NOT have to backup everything and reinstall.

Thanks in advance.

If you've been using Time Machine, you can restore your system back before the updates were installed. However, before we blame the updates, let's open
your Activity Monitor.app and see what's going on. The activity monitor application can be found in applications, utilities. Look at it closely and try to see what's using the CPU. It may be something that's using excessive CPU time that's causing the slowdowns. Let us know.