I know folks moan about Norton products, calling them bloatware, etc., but I have found NIS to be a pretty stable and reliable product on my Win XP and Win 7 machines - configured correctly it doesn't slow down games or complex apps like video editing suites and it seems to do a decent job at protecting my machines. It's not foolproof, but is any antivirus and firewall 100% foolproof? Combined with occasional use of freeware malwarebytes, NIS has kept my netbook and PCs safe for the last 5 years, although I do backup to be on the safe side. You can use the software in full auto mode or delve into the advanced options and settings if you want to tune it - this can be useful if you run very hardware-intensive games or applications.
Norton's own renewals are rather costly, so I always renew by buying a licence from Amazon. I used to order a boxed product but this is now easier than ever with this download product - Amazon send you a new licence code in the purchase confirmation email. So if you already have NIS installed you can just update the licence from within NIS with the new code and there is no need to download anything from Amazon. In fact, even if you don't already have NIS on your machine, you don't have to download it from Amazon's download link - you can just download from Symantec's NIS web site and then enter the licence key that Amazon sent you. So all in all it took about 5 minutes to renew my licence using this download product - just had to wait for the email from Amazon.
So, to recap - I have found NIS works well on Win XP and Win 7, it can be tailored to suit different users (left on full auto or tweaked), and used within a strategy of occasionally running other scanners like Malwarebytes, it seems to do a good job at keeping a PC safe.