You can clone the old drive to the new one then swap the drives, making the new one master and the old one slave. Macrium Reflect Free
will do this.
Are the hard drives SATA or PATA (IDE)? If PATA then you install the new drive as slave and make sure the old one is master. There is a tutorial for using Macrium
for normal backup and it includes creating a REcsur CD which I think you will need to clone the old drive to the new one. If SATA connect th4e new drive to port 1 if the old s on port 0.
Once cloned, remove the old drive and make the new one master. Make sure everything still works okay. If yes, then you can connect the old drive as a slave and use it for storage.