How can i wipe out my whole drive?

How can i wipe out my whole HD, i just installed Win 7 on a new hard drive, installed it but made three partitions, had an extra 300GB which magically disappeared, and i sent some files to drive E: but i couldent delete them or remove them. I think the simplest way for me now is just to delete all the data and start up agian, what program can do that for me (preferrably free)