I have a MAc OS , now i wanted to know How to Fix Bad Sectors on a Hard Disk?

If no good you can try using disc utility from the install disc [start while pressing 'c']

You can use a software like techtool which can help a little more sometimes, again as a last thing can boot from the techtool disc & try again.

If this doesn't do it then you can reformat [erase - same thing]the disc on the next tab on disc utility. Mac osx extended [journaled is usual for osx, but don't tick the os9 driver box [unless you need it.
If this doesn't do it the keep an eye on it as it's not 100% healthy

1. If you're running Mac OS 9.2 or an earlier version, search your hard drive for a file called Disk First Aid. You can use this Apple-supplied utility to verify and repair disk errors.
2. If Disk First Aid says it can verify but not repair your disk because it's the startup disk, you should restart your Mac from the System CD-ROM disc that came with your computer. Hold down the C key during startup to force the Mac to start from the CD-ROM. Older Macs, pre-G3, need to press the Command- Opt-Shift-Delete combination.
3. If Disk First Aid fails to fix all the problems it detected the first time you run it, try running it a few more times
4. If you're running Mac OS X, you'll find that Disk First Aid has been made part of the Disk Utility program, which you'll find in the Utilities folder in the Applications folder. Click on the First Aid tab after launching Disk Utility.