Back when I was more involved in the Newsgroups (which I assume you're referring to), I always used Forte's Free Agent newsreader client. It looks like there is still the free version available at their website:
http://www.forteinc.com/agent/download.php - it includes both versions in the download I believe, the Agent and Free Agent package.Mozilla Thunderbird also offers newsreader capabilities, however I've never used it myself. More info here:
http://www.mozilla.org/products/thunderbird/Google Groups is also a limited online option. Info:
http://groups-beta.google.com/Hope that helps.