If you are interested in trying Norton Anti-Virus 2011, you can download it for a 30 day trial from the Norton site, or from CNET. Downloading it from CNET does not require you to give credit card information, so it is the wiser option if you are not sure you will keep using Norton as your anti-virus software.
If you do download directly from Norton, as Donna notes in her comprehensive review of Norton AV 2010, Norton will bill your credit card if you forget to cancel within the 30 day trial. This is known as an opt out trial, and I endorse her suggestion that you try it through CNET without providing credit card information.
Norton does have a number of their programs available for free trials, if you are interested, and they are detailed in this article, along with explanations for each.
There are other anti-virus programs available from well known companies, and you may find you want to try a couple before deciding on your final protection decision.
Just remember that you should download your new software to your computer, so you can install it as soon as you uninstall the security software you are using. Do as much of the installation as you can without an active connection to the Internet, so your computer is not surfing the net unprotected.