I work for a State agency as an IT Tech, we have a fund raising foundation that also connects to our work network. They have been using the AVG Free for years and have had no infections from viruses (15-20 computers). They have had one computer infected with XP Antivirus 2010 (Now 2011) Malware. We use 2 different AV products (one for our email and Mcafee for our desktops) while we maintain about 10x more computers, we have had no infections on any of our computers in the last 5 years.

AVG Free is a pretty good product and would do well for how you intend to use it. But Mcafee would also do a fine job as well (although it cost just a little bit more, LOL)