How do I make an old computer secure?

[lurker17260]

I've got an old computer that doesn't work anymore.  I have found that my local tip will take it, but how do I make any files etc on it secure before I throw it out?  I remember something/someone saying you should destroy the hard drive. 

I'm no techy so have no idea where or what I should be looking for.

[annies_fancy_dress]

Get a backyard bonfire going while it's still winter and toss the pute in.