Also try AVG Free 8.5 Virus protection at:
http://free.avg.com/au-en/homepage
Nev, delete IE from your system through
Control Panel > Add or Remove Programs
I have used it for many years, as has many of my family and friends and it has always had good reviews. I run it every week and it picks up and cleans my systems. I've never had any issues.
My system is Windows XP (one of two licenced products on my computer, the other being Acronis True Image). All the rest , including Firefox and Thunderbird, are open sourced applications.
Note: I tried Ubuntu for a while and whilst I enjoyed it and it worked flawlessly, it does take some getting used to, and in the end I reverted to Win XP Home because I know more about how XP works than Ubuntu.
I also run Acronis True Image, which has to be the most simpliest "ghosting/imaging" progam around. I made several ghost images of my PC at varous stages of my XP installation and I ran revert back to any of them within seconds.
For years, I've never had one issues with my PC, not one. No hang up's, not blue screens, no viruses - nothing!