I can get on Usenet on Mac OS X using Lynx, and I can get on Usenet on Arch Linux by telnet'ing to telehack.com and issuing the usenet command. But for some reason, I can't get on Usenet using either Ubuntu or Debian. I've tried Lynx and I've tried a couple of dedicated Usenet clients (I think tin and nn), but I can't seem to reach any news servers. Why is this?

I used the command you supplied
and it connected just fine.

Maybe your IP is blocked there?

Did you set /etc/nntpserver or $NNTPSERVER? I use "tin -r", and that works. Do you have a ~/.newsrc file? trn, pan, emacs, slrn, and the built-in Mozilla readers you can also try. Also note, there's not too many real NNTP servers open to the public anymore for free. One is nntp.aioe.org. The web, with its "let's just bolt everything on here" approach, because few are capable to work anything other than a web browser mentality, have all but killed USENET. I suspect a configuration issue, rather than a network one, short of you being firewalled off from all but the web and dns.

"telehack" is a simulation of an old-time network and isn't USENET at all. http://telehack.com/telehack.html