Well if your on 10.5.8 like your signature says, then you have bigger problems to worry about.
10.5 isn't supported anymore, so you might as well attempt data recovery (if you dont' have a backup) and call Apple via phone for the 10.6.3 white retail disk.
Then follow this proceedure to erase the ENTIRE disk with Zero's and install 10.6.3, then Software Update to 10.6.8
10.6 will run your older 10.5 software and hardware drivers using Rosetta, but 10.7 and 10.8 will not (also requires more RAM and will slow down your machine)
Over 50% of OS X users are on 10.6 and Apple is supporting it with security updates etc. so you should be good with your present software etc., until you need a new 10.8, 10.9 etc., machine.