Clone a damaged disk first
One of the problems with a damaged hard drive is that it is usually unstable. Trying to fix the damaged disk can do even more damage. This is especially true when using programs that automatically repair FAT tables, rebuild partitions or fix the Master Boot Record (MBR) automatically. One cheap piece of insurance is to copy the damaged disk to another disk and work on the copy. Unlike a conventional disk copy operation this kind of cloning involves copying the drive image sector-by-sector using special software that bypasses the operating system's copy utilities with their parity checks and such. The goal is to take everything on drive A and put it on drive B whether it makes sense or not. There are a number of third-party utilities which clone even damaged disks, such as Byte Back from Tech Assist Inc.
Once the disk has been cloned, you can use your repair software's automatic rebuild facilities or examine potential trouble spots, such as the (MBR), and attempt to repair damaged sectors yourself with a media editor. If you can't recover the information, at least you're not making the problem worse.
About the author: Rick Cook has been writing about mass storage since the days when the term meant an 80K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last twenty years he has been a freelance writer specializing in storage and other computer issues.