Perhaps you need to format it first.
I haven't done anything like this for a while so might not be on the money here but if you are installing the OS on to a blank brand new HDD, I think you insert the install media, hold C or what ever it is to make it boot from CD and then once you get to screen to do installs, click on Tools and choose Disk Utility - from here you can format the drive into a Mac Format.
If you are adding this drive to an existing mac (internal or external) and what to copy one drive to the other (for example) then again you need to use Disk Utility. In Leopard, press Command+Space and type Disk, this should identify Disk Utility , click on the app in the spotlight search results.
From here you can partition and format the new drive.
It will probably appear in the left hand side as WD and then a model number, click it and the right window should offer a button partition. From here you can select all or part of the disk, give it a name (if required) and select the formatting you'd like to use - probably Mac OS Extended (Journaled).
Once in Mac format, superduper etc should be able to copy or restore an image to it.