Is there any information on the old drive you want or need to save? Assuming the old drive is SATA - the connector should look like this:
- it should plug right into the new system (power off and uplug the new system when interesting the old drive. You won't have to do anything to get Windows 7 to see it then. If there's data you want to save, copy it onto the new drive. Then format using Explorer. Go to Computer, and right-click on the old drive, and click Format. Make sure the box that says "quick format" is checked or else the long format will take a very long time.