Free Linux based home anti-virus/spy/adware proxy?

JaBob writes: Would anyone know how would to go about setting up a linux distro as a home firewall/antivirus/antispyware/ad blocking proxy? I have been wanting to play with a linux box more and more, and I'm sick and tired of fixing my family's windows boxes from the crap that they download. Is there some kind of free proxy solution that will also scan incoming files and extensions for malware and other garbage? I know I can't get them to switch to linux, because some of the apps we depend on don't work on linux, even under wine. A simple Google search yields quite a bit on using Squid to filter ads http://www.google.com/search?q=squid+ad+block , but I have yet to find any information on using it as a filter for other things. I have played with MS ISA server 2004 and would love it if there was something similar or better. I'm a bit of a techie (mechanical engineering student that used to major in CS), and don't mind having to learn a bit to get it set up and working properly, but I don't want to have to think about it and write it from scratch myself (no time, insufficient skills). I could really use a bit of help from people who are a bit wiser and more experienced in this than I am. Thanks.