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.