Wiping an HDD clean of data

Alright, I plan on wiping this old laptop my parents since they keep asking me to do so since Vista is fucking horrible. Will simply formatting the hard drive wipe everything clean off of it or do I need something like Derik's Boot and Nuke (DBAN) to get rid of everything?

Also, off topic, but I have a Window's 7 disc lying around and used it on my gaming PC. Am I going to be able to use it again or do I have to call Microsoft to ask for another CD key?

I'd use Gparted, or DBAN, if you're more comfortable with it. Wipe the partitions, delete the partitions, then format the drive a couple times.

You can use the disk again, but it isn't guaranteed that the key will work.