Click on the 'hammer' icon, at the top of your mIRC screen.
On the left side, there is a list of settings. Choose 'connect'
For Full name, type whatever name you'd like to go by.
For Email address, just type in any email address
Underneath the spaces for your nick, it should say: 'Server: Undernet - [server name]. If it doesn't you need to change it. Click on the orange button, and look for IRC server. Click on the drop down menu, and choose an Undernet server, near the bottom of the drop box and not an AustNet server. Click connect to server to try these new settings.
You can also use the web-based chat client at http://www.undernet.org/webchat.php.
You will need Java installed for this, though. To start, just type in your name, and your nick. For channel, choose 'Another Canal'. Press connect, and wait while it loads. Once you see 'You are connected to the Undernet (or something similar) you can type /join #lanekent