NIS 2010 Upgrade question

I have NIS 2010 on 2 computers with a 3 PC product key. Can you confirm that I can upgrade them to 2011 by running the NIS 2011 install file?

 

To use my spare license on a 3rd computer should I install NIS 2010 and then 2011 on top? My concern is that if I only install NIS 2011 my product key won't work.

 

Is it worth to replace NIS with 360?

 

Thanks for your help and happy holidays.