Upgrade NIS 2009 to NIS 2009

Have 30 days left on my NIS subscription.  Just bought NIS 2009 at Staples since it was on sale with a rebate.

Got home and realized I already have NIS 2009 installed.  

Before I open the box, since this is a different disk, will it install as a new subscription or give me a problem because of the same version?