I recently had one of my home PC hard drives fail. It was in a striped raid, so I had to rebuild the raid (no data lost, only the OS partition was there). Is there any way to diagnose exactly what went wrong with the drive? That is what caused the failure? Also, in general, what is a good way to dispose of a failed hard drive securely and realistically (I don't have thermite or muriatic acid)?
As for figuring out what happened. Honestly, it's most likely a physical thing, which is really hard to diagnose those. It could range from dust to thermal temperature.
For cheap disposal, use a hammer. Seriously, if it's that much of a concern, you're gauranteed no one will get to your data! But, if you want a more software approach, try http://www.killdisk.com/.
I've heard good things about SpinRite for this sort of thing, but it's a little pricey ($90)
I think there is an interesting add on to this question at Bustadrive, a home-made hard disk destroyer.