need help upgrading from NIS 2006 to current on Windows 7

I have NIS 2006 installed on an old pc.  I have the original installation file saved on an external drive.  I just finished building a new pc w/ Windows 7 (64-bit).  I tried installing NIS 2006 onto the new pc, but Win7 told me that the version is incompatible.  So where do i start?  I think I remember seeing a pop-up on my old PC telling me that I could upgrade for free.  The only downloads that I see on the Norton website all want me to pay.  Thanks for your help!