All messages you send to Usenet include your IP address in the technical, usually invisible, part of the message, called “headers”. Here’s a good article about how to read and understand them: http://www.technomom.com/writing/usenetheaders.html
If you participate in Usenet discussions, then quite a lot about you can be learned from analyzing them, and even if you use different nicknames, the IP address will be the same everywhere (provided that you use a broadband connection; if you use a modem, the IP will be different every time you connect, so the problem won’t be so serious). Since the IP address gives any hacker the starting point to try and get into your computer, quite a few people are interested in hiding their IP address from public Usenet discussions.
In order to post an untraceable message you could use a so-called anonymous remailer (which would work for email too), a service which receives the message from you, strips out all original headers together with the information about your location and IP address, and then re-sends the message to its final destination. This approach is often inconvenient and unreliable. Using A4Proxy for the same purpose is much easier.
Although A4Proxy doesn’t work with ordinary newsreader software like Forte Agent or Outlook because these programs require protocols that are not supported by A4Proxy, you can still send anonymous news messages using web-based Usenet services like http://groups.google.com. When you connect to their web interface through A4Proxy and send the message using their web forms, your IP address is hidden from them and it is not present in your postings.
We also have a new anonymizing product, AntiFirewall, which allows you to read and post to newsgroups anonymously with ordinary newsreader software like Forte Agent. Please have a look at http://www.antifirewall.com for more details.