Hi I am kaniz,
I was wondering if you would be able to tell what I should do to delete everything off my hard drive leaving nothing behind on my windows vista because I am selling it.

You would have to reformat the hard drive to effectively erase everything on it.

Your Windows Vista machine came with a Recovery CD or partition. Using this will restore your PC to the condition it came from the factory.

If you Reformat or shred the disk, as suggested, you will need to have a OS disk to put an OS back on the machine.

If you are truly worried about leaving any files on the hard drive that might survive a formatting just buy a new hard drive and destroy the old one, it's the only 100% guaranteed way that none of your data can be recovered.

Hard drives are not all that expensive if your not buying top of the line...

You can simply do this...
Insert your OS boot cd
Boot with cd
In preparatory screen appears, in it delete all partitions
Then restart your system and remove your boot cd
Hard disk will have nothing on it