Replacing Anti-virus with Internet security 2011 (already purchased)

Hi there,

I have Norton Anti-virus installed on my home PC (Windows XP) that only has a few days left before it expires, and I have purchased, (from Amazon) a Norton Internet security 2011, not download, but with CD!

Can any one out there give me any 'tips' where to start with the installation?

I tried just entering the New 'Product-key', but it didn't like it as it was for Internet security, and not Anti-virus.