Formatting external drive in Mac

[Simon Cavendish]

Dear Listers,

I have an external usb drive onto which I've been backing up via Time  
machine. I will now be switching to backing up wirelessly and I would  
like to use the usb drive to create a clone image of my mac using  
Super Duper as has been suggested recently on the list. I understand I  
could boot up from such an image.

The question I have, given that I've been backing up onto the usb  
drive via Time Machine, do I need to reformat it in order to put a  
clone image onto it? How does one reformat an external drive on the Mac.

Thanks listers for any help. I know it's probably a very basic  
question for you.

With best wishes

Simon