This is one tool you should keep in your toolbox if you are hardware DIY enthusiast. Recently I undertook a project to increase the storage capacity of my Xbox by reusing an old hard disk and had wanted to be sure that the dusty piece of metal I pulled out of my basement store is still in acceptable working condition.
Yes, I can try plugging it into a Windows rig and run chkdisk. That will let me know whether the drive is functional. However, it doesn't tell me if the drive will fail anytime soon. For that, you will need a tool that can read the S.M.A.R.T. statistics that are stored on the drive. Hence enters Data Lifeguard Diagnostic from Western Digital. (Did I mention its free?)
This tool not just allows you to view the statistics (and drive information like serial number, model, etc), but you can also run tests as well as zero the platters for security. There are two types of tests it can perform, a quick overall test as well as an extended test which does a full surface scan.
There are three versions available on the website; one that runs on Windows, another that runs in DOS mode and is packaged as a bootable floppy disk, and the last runs in DOS mode but is packaged as a bootable CD. The last two options obviously work best when your primary hard disk is giving you problems.
Best of all, its free and it works on other brands of hard disk too!