Given that these A/V products are only marginally effective, does anyone have any suggestions for what might be the best bang for the buck in terms of protectio

Given that these A/V products are only marginally effective, does anyone have any suggestions for what might be the best bang for the buck in terms of protection a Win7 machine? My preference would be just not to run windows, but it's my mom's system, and she needs certain windows based accounting packages...