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.