A question about 2010 Antivirus install?

Hello, I recently purchased a new sony vaio laptop from best buy which came with 30 day trial of norton internet security. This trial has expired and i purchased the 2010 antivirus software from my college bookstore; however, when i tried to install the software from the cd yesterday it told me that i already have a "better" version of norton running on this machine. This is confusing me because for the last week i have been getting "subscription expired! your no longer protected against viruses and malware!" messages.... I am not sure what to do, do i install the lesser product and if so will it remove the norton stuff already on my pc or do i need to do something else to get these expired messages to stop displaying? 

 

Also i would have bought the license for the software trial version but i just couldnt afford to spend 100 bucks on AV software(broke college student) ty for any responses.