Recovering data from a failed hard drive.
 

First the tip, then the story.

If you have a hard drive go bad on you, as in the computer doesn't even boot past a "hard disk failure" notice, Linux might be able to help you.
Having this problem myself, I found a post on Google that mentioned the fact that it is possible to shut a secondary drive off in the BIOS and possibly still access it from Linux. By doing this I was able to boot the system with no disk failures and copy files from the hard disk.
(Can't find the link again so no direct thanks to the poster. Although I will mention that this helpful hint was as a follow up "how I solved this problem" to his own original question. A reminder that it can be very useful to post how you did solve your problem.)

The sad story:
Thursday AM, the hard drive in PC1 dies with a "click click" sound and the computer freezes. That evening, running the manufacturer's disk utility confirms a bad drive.
I think I am sly switching to PC2.
Saturday PM, PC2 freezes up. An old drive I had installed as a secondary has also failed and at the same time the main disk suffers partition corruption.
All systems dead and down.
Sunday. I am online only by the virtue of Knoppix. I discover PC2 has a power source problem causing constant rebooting when running Knoppix from CD and using the swap file from a hard drive. I discover Knoppix complains about an unrecognized network card in PC1, even though it is the exact same card I have in PC2.
Finally I reload Debian on a working (knocks on wood) drive and begin transfering files as suggested above.
Now I must be the insane backup man for 6 months (telling everyone they must backup all their files daily with multiple copies).

Such is life.
Good luck with your bad drives.