20"/24" iMac hang at desktop?

Question

We have three 24" iMacs here at work, and one 20". The 20" and two of the 24" iMac's have hung at boot up, all at the same place.
As soon as the desktop starts to load, the Spotlight magnifying glass comes up then the machine sits there and stops booting (the mouse can move). All that is visible on the screen is the solid blue desktop, and the magnifying glass (with that tiny bit of menu bar behind it). The rest of the menu bar and the desktop do not load.
The machines don't do this consistently, nor do they do it often. I'm thinking it's bad memory, since the one thing all the machines share is that they have one stick of apple memory (1GB), and one stick of edge (1GB).
All the machines are in 10.4.10, latest iMac updates installed (1.2.1).
Any ideas?
Thanks all!

Answer 1

I think I may have found the solution.
It sounds like the "hang at desktop, only the spotlight icon comes up" is part of a font cache corruption. This would make sense because the machines that have hung are all using the same fonts stored on the network. This would also explain why I have seen this behavior on some of the older OS X machines we have.
The fix appears to be deleting the /Library/Cache/com.Apple.ATS font caches in single user mode.
The other fix is to boot into single user mode and run applejack (applejack.sourceforge.net) to clean up the caches.
I'll post here if this is successful.