Have you ever downloaded a file and questioned if it was virus or trojan free? Why not scan it with dozens of scanners at the same time for free? Of course, this still doesn't guarantee that there is nothing harmful in the file, but it may make you rest easier.
Simply go to
http://www.virustotal.com/ and upload your file to be scanned. You can even email the file or download an uploader client to your PC.
If you are in charge of administrating a network,
OpenDNS really can help you take charge of your network. Not only are they claiming their service is faster than your ISPs, but they add functionality beyond anything any ISP I am aware of offers. OpenDNS provides the ability to block certain domains, phishing sites, and adult sites. They also offer graphs and reports to help you see your usage. Considering the price, it is worth a look.