I used to use Norton Internet Security 2005 and this slowed down my PCs performance drastically (my PC has a similar spec to yours). For this reason (it was becoming unbearably slow to open even the smallest of tasks) I switched to some of the free utilities recommended on this forum. I currently use AVG Antivirus, ZoneAlarm(firewall) and Microsoft Windows Defender (anti-spyware). So in answer to you question 'is Norton to blame' then I would say yes from my experience. As for other utilites that SystemWorks includes and their alternative counterparts, I'll leave that to other forum members!