IDS/Virus Detection
 

Is there any software that I can run on my NAT firewall to detect local clients with viruses/worms? I know Cisco has a commercial product used by my school, but I was wondering if there were any programs that can do analysis of the traffic through the firewall. I'm not sure if ACID has this capability or not, but I have been looking into this.

Mmm... I guess you can try Snort. It's THE IDS for Linux

you can also scan the traffic going through the gateway to stop viruses from getting into the local network with something like viralator, for example:

http://viralator.sourceforge.net/