My advice to the OP, for what it’s worth, is to get and install a free newsreader (best not to use Outlook Express, although many do) such as Free Agent for Windows. Check with your ISP for their news feed facilities and configuration (aka “NNTP”, aka “Usenet”) and spend a few minutes playing about.
Configuration is a doddle - you just need the name of an NNTP server (most ISPs have something like nntp.myisp.news, even if they don’t host it themselves), possibly with a username/password combination. In many cases, if you’re using your ISP’s feed, you don’t need the latter, since simply being connected to your ISP is validation enough.
Once you’ve got that set up, the first step is to download a list of newsgroups into your newsreader. There are many thousands of groups, mostly inactive. Once you’ve got the list, you’re free to browse around and read messages. Finding a group dealing with an interest of yours can be a little fiddly, since the naming conventions are quite odd.
You might want to look at alt.fan.cecil-adams, as Struan points out. If you like the SDMB, you’ll probably enjoy this one, since it’s a bunch of clever people (and the usual handful of idiots) with similar interests to the people here. Fighting ignorance, all that - a ragbag collection of threads on all sorts of topics.
Without knowing more about what interests you, it’s hard to recommend anything more specific than that, but you’ll probably be surprised at the diversity of special interest groups. Have a thick skin, because there is a lot of rubbish out there, but time spent sieving through all that is time well spent. Expect a lot of very good tech support groups, loads of humour, a fair spread of regional and non-English-language groups, sex, health, conspiracy theories, computer gaming, well, something for everyone.
If you find a group interesting, your newsreader will have a ‘subscribe’ function. All this means is that you’re telling your newsreader to keep that group up to date; in reality, you’re not subscribing to anything.
Lurk at first, until you’re comfortable with the customs and practices of each group. Before your first post, subscribe to alt.test and make a post there. Then check to see if your post comes through. No-one really uses alt.test for any other purpose than to check their own posting setup - that’s why it’s there.
All of this is free. You only need to pay for anything if you want to take it much further, and have access to binaries, or a more fully-fledged newsreader.
Simultaneous posting means additional feedback:
You’re ahead of me, it seems.
Thunderbird’s OK - I’m not a fan myself, but plenty of people use it. Don’t restrict yourself to the first 500 unless you’re on pay-per-minute dialup or something - the headers are tiny. I generally get all available messages for a group I’m subscribing to, even if it takes a few minutes.
If you find inactive groups (as you seem to have done), move on and look elsewhere. Most groups only get spam and rubbish, but the gems are there. Trial and error (and a bit of Googling) should get you what you want. A good idea is to search in the “Groups” part of Google, using keywords indicating your interest. This will show you the history of relevant Usenet posts, from which you can get an idea of which groups might suit your purposes.
Good luck!