Wiping Old Hard Drives

[Skywarp!]

So I have a new computer and I'm getting rid of the ol' beast. I know a hard drive "shredder" program is recommended--something that will wipe the drive and overwrite it (preferably overwriting it three times) by scrambling data on top of the old data. Which programs do you recommend to remove all sensitive data and turn your old computer into a tabla rasa before putting on the curb/donating it?

 

Or should I just use the power tools method--taking the hard drive out of the computer and pulverizing it with a hammer? Perhaps a combo of both? I guess that's the fail safe way...

 

Thanks in advance.