I found a free decent-feeling IRC client; HydraIRC. You can get it here:
https://www.hydrairc.com/. Go to "Downloads", scroll down to "Binaries" and select "HydraIRC.exe". That's the easiest way.
Here's how you set it up (after you've installed it):
1. First it asks you to create identities. Do that. In the Preferences dialog, click on "New" and fill in the information. It's enough to fill the four topmost entries. Click on "Add" to add your nickname to the list. Then "OK" and "OK".
2. Go to File->New Server
3. Click "Add Network", type "AfterNET" and click "OK"
4. Click "Add Server"
- Description: Random server
- Address/Port: irc.afternet.org, 6667
- Network: AfterNET
5. Click "OK" and "OK"
6. After a while the window should fill with red text. Now enter the following command: /join #pianoforum.net
When you want to join the next time select "File->Connect" (or press Ctrl+S) and then "AfterNET->irc.afternet.org" and "OK". When it's ready, enter: /join #pianoforum.net