Depends what you want to do. Most hard drive manufacturers have utility (available from website if not provided with drive) which will copy existing drive as is to new drive (so should be able to just make it primary master, and run as old drive). So, if that's what you want to do - problem solved.
If you just want to mount new drive as slave and use it as a data repository (eg, music/video files) - just use explorer to copy them.
If you've something else in mind - please post back.