A year and a half after debuting its first Zune, Microsoft is finally going after the TV download market with its portable media device via a software update that will bring this and a host of social networking functions to the table.

Microsoft ventured into downloadable video sales for the Zune late last year when it released its second-generation players and software, but the content was limited to music videos. As of today, however, Zune Marketplace will start selling TV shows for 160 points – or about $1.99 – from a variety of networks including NBC, Nickelodeon, Comedy Central and Cartoon Network.

In addition to the new video offerings, the Zune 2.5 spring update brings new features including the ability to subscribe to a friend’s music playlist, gapless music playback (finally!) and playlists that automatically update themselves based on criteria set by the user. The update should go live today and you can get it through the Zune software installed on your computer.