I’ve noticed Joost tends to not refresh the content of their channel Line up unless it resets its User Profile.
I’m not sure if this trick works on Windows, but it certainly does work for Mac. (Please leave a comment if it works the same way on windows, I don’t see why not, all they have to do is check for the alt-key modifier as the application starts up, should be the same thing)

1. Close Joost if it’s open
2. Hold the ‘Alt’ key and Click on the Joost Icon
3. You should now see a dialog to reset your profile

Having done this, all the newest Channels and existing channel lineups should be refreshed.
Enjoy

About Joost
Joost (pronounced /j ooːst/ “Juiced”) is a system for distributing TV shows and other forms of video over the Web using peer-to-peer TV technology, created by Niklas Zennström and Janus Friis (founders of Skype and Kazaa).

Joost began development in 2006. Working under the code name “The Venice Project”, Zennström and Friis assembled teams of some 150 software developers in about six cities around the world, including New York, London, Leiden and Toulouse. According to Zennström at a 25 July 2007 press conference about Skype held in Tallinn, Estonia, Joost has signed up more than a million beta testers and is on track for an end-of-year launch.[1]

The teams are currently in negotiations with FOX networks. It has signed up with Warner Music, Indianapolis Motor Speedway Productions (Indianapolis 500, IndyCar Series) and production company Endemol for the beta.[2] In February 2007, Viacom entered into a deal with the company to distribute content from its media properties, including MTV Networks, BET and film studio Paramount Pictures.

Source: wikipedia.org