How must I deal with anti-virus software on Windows 7
Solution 1:
Is it safe? Well, that depends on how you use your computer (I'd guess you browse, download applications, in which case, no, it's not really safe). For what it's worth, nowadays most AV's are less system hungry, are free and you will barely notice them running. For the small download and small maintence it just makes sense too.
This guide shows how to install security essentials and other information regarding viruses. Security Essentials is a solid AV.
Solution 2:
1: NO. No matter how safe you think to be in you internet habits you still have to run a virus-scanner.
2: No, Microsoft Security Essentials is not mandatory, but....
3: Security Essentials is one of the best free, fast and light-weight anti-virus programs so you might as well use it anyway. Of course: It does require a genuine Windows installation. I hope you have one.....