once a drive starts to make clicking sounds, it is only a matter of a short while before it stops making any sound at all!
Although you have told us what version of OS X you are running, you did not tell us what model of Mac you have.
Depending on the model, I suggest that you take the old HD out and replace it with a new one. Purchase a firewire case for you old on and connect it to the Mac.
From there you can attempt to recover files from it.
Your computer itself is almost certainly still in working condition, it's just the HD that is bad.
I have a Mac OSX 10.4.11 desk top, couple of days ago I started having problems restarting it from sleep mode, it would make a clicking sound and stay blank. Id have to turn it off and restart it that way and it would be fine. How ever it has started making a clicking sound and I was getting a flashig file with a question mark on start-up. I am now scared to turn it off. My computer no-longer reads discs or portable Hard drives. Im thinking its on its last legs but I need to back-up my files any suggestions please I am all ears.