I would like to put a workstation XP/Other with some sort of software on it that allows me to configure it to filter traffic coming into or going out of our network. Basically to filter out certain web sites, or certain types of protocols. We are behind a firewall and router, but locally do not have access to them in order to do this. Hence the idea of putting something between the firewall and switches. It would be a bonus to perform other functions, filtering spam, etc.
What suggestions are there for doing this?