Since people are having trouble logging into the Justin.tv (JTV) chat via IRC clients, I'll explain how I was able to log in via mIRC. I know that Grifforzer was able to do it in a different manner than this, but whatever works is fine!
Official Guide:
http://www.justin.tv/p/irc_guidemIRC is capable of connecting to multiple servers (i.e. Ustream and JTV) at the same time. Just open up multiple mIRC windows. Alternatively, you can go to File -> New Window to make multiple server tabs within the same window. Credit to Eat_Box for the tip!
For the most part, follow Foxtrot's tutorial with the following changes:
Part 2: Put your JTV username in the fields
Part 4: Make sure you put in your JTV password
Part 11: Either "thetombobblendershow" or "#thetombobblendershow" will work

After everything is finished, click the lightning bolt. You should get something similar to this:

If you're successful, then you'll immediately connect to the chat!

If you're still stuck, don't worry! Leave a post describing your problem and we'll see what we can do. Thanks for watching The TomBobBlender Show on JustinTV!
One more thing: If you start to see double posts, just restart mIRC. It happens occasionally.