HELP!! /usr file accidentally deleted!!

I was cleaning up files on my iMac (Leopard) and i accidentally deleted the /usr file (which for some reason was not hidden)!!
I tried to restart but it didn't work. I then tried to reinstall the Leopard software which got it working again but now system preferences wont open (it says 'not responding' and refuses to force quit).
Would someone please give me some advise as to what to do as I'm really stuck.
Thanks

/USR is not a file, it's a folder which houses many sub-folders. How did you manage to delete it? I'm assuming you also then emptied your Trash?

You need to properly re-install Leopard in order to get back that folder and to get your system working again. I guess you didn't have backups either?

Boot your iMac with your Leopard DVD and re-install using the "Archive and Install" feature. See the following link.

After you re-install and get your system back up and running, buy an external hard drive and use Time Machine to backup.

Regards.

Thank you for your help, my iMac is working properly now.