not all hard drives are that easy though, if you have an older hard drive that has an IDE interface (the thin/wide cable) you have to check the jumper settings near where the drive's data and power plugs are and make sure that one is set to master and the other is set to slave if you're running more than one...1. You can use your OS install CD. Boot to the CD and just go through the motions to get to the point where you can delete and reformat the partition/drive.
You can also use a program such as Kill Disk or DBAN
How to erase my hard disk drive and start over.
2. Well, kind of. They are in that you just connect them to the mobo and power and they're ready to go.
I've seen "cable select" jumper settings do some absolutely retarded things on hard drives and CD/DVD burners, I always set the boot drive as master and the other hdd(s) as slave and have never had a problem...In some cases with ide drives the second was set to cable select rather then slaved depending on which older version of Windows you were running at the time as well as who it was made by. But you first have to see any drive already set up and accessible to place anything on it to be wiped.
The question there however was how to wipe a drive already in use. That could be for removing any OS along with data simply to see another OS installed on a new primary.
Presently the betas for 7 lack the option of deletion as well as partitioning and formatting while still providing the custom install option once an existing partition is selected. That rules out booting from a 7 dvd at the moment for that. Drive partitioning tools like GParted(free), Partition Magic if not any zero filler like a security tool are still the common methods.