Maria, I'm not too sure your problem had anything to do with the thread you posted in so I gave you your own and re-titled it.
We can't help with sales questions here. You'd have to subscribe to McAfee online here: http://home.mcafee.com/Default.aspx?culture=EN-CA or go to any PC shop and buy the product there.
You would have to remove Norton first and use their removal tool. Support for Norton products is here: http://www.symantec.com/norton/community/