You are experiencing the CS4 Critical Memory Bug. Nothing to do with your computer. Adobe does not care to provide an update to fix it. The bug was reported right after the version release. Adobe refuses to fix anything.
Its important to realize that Illustrator is a 32-bit application. What this means is at most it can access just under 3.2GB of RAM and no more.
Here are some step that can help you a little bit:
I hope this helps!
since this is happening on several machines at the same time it is possible the font cache has become bloated
there are applications, some free to delete the font cache files they will be rebuilt by the system.
There could be common plug in used that is causing the issue.
You could also have a small amount of space on our scratch disk and or the scratch disk can have permissions issue like only allowing the administrator to use it, you may have to reset the permission. On the windows platform it is a manual task I believe.
You might want to at some point install a dedicated scratch disk which would also be good for Photoshop.
I have an internal RAID 0 on my Mac for that purpose.
4 GB of RAM sounds fine but if your computer can take more then you that might be good as well.
But certain Window based computer and oS can only use the 4GB limit. You have to see how much your computer and OS can handle.