|Some people still like Norton... I do not know why.|
At work, we still have some P4 machines running XP, some came with 256MB RAM or less, all now have 512MB, 768MB, or 1GB and many of the boards will only handle up to 1GB, some 2GB, 3GB could not happen. These run very well on Avast and like many older systems, will be bogged down by any version of Norton (if someone would want to waste that much money). Norton would also need a core to itself, but most of these still running XP are P4's and other single cores, and even if someone had a core 2, who would want to waste a core and half their memory just for an antivirus program that delivered only reasonably moderate protection? Even if they 'cleaned up their act', they are 2 generations behind the best that is out there. At home I use Webroot Secure Anywhere and it is the least intrusive antivirus program I have ever experienced, uses resources intelligently, and no longer needs continuous updates and scans. Even their old program that I ran for many years on XP systems, ran fine on 512MB RAM (before IE7 and everyone needed more memory) with only minor slow downs.
You have to be a little bit crazy to keep you from going insane.