Many IT Xpress customers use MS Security Essentials for the anti-virus protection. It's lightweight and just 'works' as good as any AV program can. A new release (v4) just hit Windows Update that has even better performance and a simple user interface. Kick off a Windows Update and it will update for you. Like if you use MSE and Share with your friends!

Microsoft Security Essentials Updates with Better Performance, Virus Detection, and Interface Change
Microsoft Security Essentials is our favorite antivirus software for Windows, and a new version is out that's even lighter and easier to use than ever.