Erase hard drives over the network?

If you have norton ghost maybe you could make a 'blank' image and then ghost that to all the computers.
First thought that came to mind.
Other than that I would say you would need to do each one individually.

we do have norton ghost but we need to make sure that the data is not recoverable for security reasons. would the blank image be ok for that?

Then the best thing to do is destroy the harddrives. To be 100% sure that the data isnt recoverable would require you to write and rewrite 0's to the whole drive on each computer which, depending on drive size, could take hours to do.
I havent used norton much so I am not sure if a blank image would essentially write 0's to the drive or not.
Maybe someone else here would know.

lol.. You can run real fast past all the drives with a refrigerator magnet,

If they are all windows based then I'm afraid youll need to use 50 floppys and zero the drives out. If not then you can shut down the kernels in unix and destroy the data that way.