watermelon, the reason to use DBAN or a program like it is because you are never really sure where on a hard disk data may be stored. Reformatting does not really remove all that has been previously written to the disk but whether or not data can be recovered depends on the skill of the person making the effort.
While you may trust your friend to not go on a fishing expedition for data on the hard drive included in the computer you sell him, you never know who will have access to the machine in the future including when your friend gets rid of it.
That’s why in some businesses like banks and law firms, the only acceptable means of getting rid of old computers includes both wiping the hard drive and then physically destroying it.
Regarding a rescue or recovery disk, these are used to restore your computer to the way it was “out of the box.” As mentioned by myself and others, when you wipe a hard drive, it is completely blank. (That means that the image mentioned by yeshivaguy1 is also gone.)
With a rescue or recovery disk, you put it in the drive and it re-installs Windows and any utilities and drivers provided for the particular computer. (This is one of the ways you would install a new hard drive although there are others.)
Some laptop manufacturers include such a disk when you buy the computer and others include a utility (usually noticeable with an icon on the desktop) so you can make your own disk. Quite likely, if you go to the website of the laptop manufacturer’s support department, you can buy the right disk for your computer.
As an example, I looked up Toshiba. They charge $24.95 for a Recovery DVD. http://forums.toshiba.com/t5/System-Recovery-and-Recovery/Recovery-media/m-p/9148#U9148
Please note: Recovery DVDs are configured so that they will work only for a specific brand and model of computer so people do not try and use them as a substitute for buying Windows.