what model pc?

You are using the windows add hardware wizard just forget about it for just now:

 

http://support.euro.dell.com/support/downloads/index.aspx?c=uk&l=en&s=gen

 

Go here, type in your service tag or select your model and the driver your looking for will be available.

Thanks for your help.  Turns out I did have the right driver, but as I was using a USB floppy it couldn't see the floppy disk at this stage.  I wrongly assumed because it worked for the first part it could use USB for the whole thing.  Dug out an old internal drive and plugged it in and away it went.  All fixed, you learn something new every day!