Do an "Archive and Install" of the OS. "Archive and Install" moves existing
system files to a folder named Previous System and then installs Mac OS X
again.
Just be sure to check Preserve Users and Network Settings when you select
Archive & Install.
Mac OS X: About the Archive and Install feature
<
http://docs.info.apple.com/article.html?artnum=107120>
Archive and Install of the OS
<
http://www.entourage.mvps.org/glossary/archive_install.html>
General advice on performing an Archive and Install
<
http://www.thexlab.com/faqs/archiveinstall.html>
This won't help with your current problems, but for future problems like
this get SuperDuper! And create a "Sandbox" partition.
<
http://www.shirt-pocket.com/>
A Sandbox is a bootable copy of your system, stored on another hard drive or
partition, that shares your personal documents and data with the original.
With SuperDuper!, you actually use the Sandbox as your startup volume. You
can safely install any system updates, drivers or programs in the Sandbox,
without worrying about what might happen to your system. If anything goes
wrong, you can simply start up from the original system. SuperDuper! has
preserved it in its original, pre-disaster state but all your new and
changed personal documents are totally up to date. Within minutes, you're up
and running again without having to go through a difficult and
time-consuming restore process.
Just a fan of SuperDuper!