Doesn't what to do depend on what the problem with the drive is?
If it is a screwed up directory or something similar, booting the with OS CD and running Disk Utility and/or booting with a Disk Warrior CD and running that may solve the problem.
However, if it is sectors dieing on the drive, I am thinking your best bet would be to get Sprinrite, put the drive in your PC and then use Sprinrite to get it into shape. Once that is done, you may still have to come at it with Disk Utility or Disk Warrior once it is back in the Mac.
http://www.grc.com/sr/spinrite.htm
-KeithP