If you are adding the new disk as a secondary drive, then you need do nothing at all.
If you are replacing the current drive with a new one, then teh procedure would depend on the type of installation you have.
If you bought the machine with WIndows pre-installed, you almost certainly have an OEM_SLP License.
If you bought Windows 7 separately from the computer, you (hopefully) have a Retail License - but this may be either an Upgrade or a Full retail license.
Machines form large manufacturers come pre-installed with an OEM_SLP Key which self-activates if other conditions are right. One of those conditions is that the proper Recovery Software is used for any reinstall.
If you don't have the proper Recovery software, then you can use a Retail disk for the reinstall, but must use the Key from teh COA sticker to be able to properly install and activate the installation - such activation may have to be by telephone.
With a Full Retail license, there is no problem - simply install with the appropriate Key and activate
With an Upgrade license, this requires that the machine holds a valid qualifying full license for Windows. To ensure this, Windows 7 Upgrade disks and Keys test for an existing installation on the hard drive. If it is not present, then the Key will be declared invalid, and the install blocked.