Sounds very interesting! The article goes on to say that in the original game, Niko did cross paths with The Lost several times, however in this, Niko only has a bit part. Dan Houser says:
This new episode, available Feb. 17 via download exclusively for those who own the Xbox 360 version (no price yet), stars Johnny Klebitz, a member of Liberty City biker gang The Lost.
"Johnny is a very different character than Niko, with a very different background," says Dan Houser, vice president of creative development for Rockstar Games. "I can't go into too much detail on the story, because we try not to give away too much plot before the game is released. But I can say that the story will show you a different side of Liberty City."
The episode, titled The Lost and Damned, requires players to have the full version of the Mature-rated GTA IV (ages 17 and older) and an Xbox Live membership to download. It's likely to carry an M rating, too.
"The story is not directly impacted by decisions you took in the main game," he says. But "tons of details and mysteries from the main story get explained, so it will add a lot of color to the main story."
Remember this is just the first of two episodes which will reportedly add hours of gameplay time. As quoted above there's no price set yet, we'll update you when we get confirmation on that but it's likely not going to be known until much nearer release. But there is a quote from Wedbush Morgan analyst Michael Pachter which says he:
[...] expects a $20 price and says Rockstar could sell 2 million to 3 million downloads. "I see episodic content as a natural progression of the quality of downloadable content."
Source: USA Today