The easiest way is to find another Mac running OSX. Restart your laptop in Target Disk Mode (either via system preferences, or hold the T key down while restarting). Connect the two machines by firewire, and run Disk Utility on the other Mac.
Repairing the disk may take some time - so don't rely on battery operation, connect to mains power.
Repairing the disk may fail, so backup a copy of crucial files before starting the repair.