NIS 2005 to NIS 2009

I have a very simple question that I can’t seem to find a simple answer to.  I have NIS 2005 loaded via an original disc. I now want to upgrade and have purchased NIS 2009 on disc.  So I have the product keys for both.  Should I uninstall NIS 2005 first (using the downloadable Norton Removal Tool for NIS 2005) before loading NIS 2009, or will NIS 2009 load OK on top of NIS 2005.  I run Windows XP SP3.  Thanks - Bob.