In general, it's best to zero-out your hard drive before you sell it/return it to manufacturer. The manufacturer will often zero-out your drive anyways upon return, but some users want to make sure none of their date is recoverable by anyone else.

This website has a few utilities you can use: http://pcsupport.about.com/od/toolso...n-software.htm

If you don't have any sensitive information on your hard drive, then don't worry about it. You can do a restore from an image/restore CD if you wish.

But if you want to get rid of your information, go ahead and either zero-out the drive or use CCleaner. Note that it does take a long time, especially if you have a large hard drive. It's a little different with SSDs, but I'm assuming yours is a regular platter hard drive.