In a major restructuring move, Neil Braun, former prexy of NBC, has ankled as CEO of upstart Internet broadcaster ICast, a position he took earlier this year.

Margaret Heffernan replaces Braun as prexy, chief operating officer and interim CEO for Massachusetts-based ICast. She was prexy and CEO of ZineZone, a venture of Andover, Mass.-based Web investment outfit CMGI.

In addition, chief operating officer Matt Farber, formerly exec VP at MTV Networks Online, has resigned to pursue other interests.

Stephen Flanagan joins ICast as senior veep of advertising sales, a new position.

Sources close to the company said ICast was formed in February with $100 million in backing to combine Braun’s television experience with CMGI chairman and CEO David Wetherell’s Web efforts to build the largest broadcast company on the Internet.

Braun has suggested that he may take legal action to counter the termination.

“I’m proud of what I’ve accomplished at ICast in a short time,” Braun said in a statement. “There have also been significant disagreements between me and CMGI regarding the strategic direction of the company, culminating in the company’s action today.”

ICast, which will be parent CMGI’s first major entertainment-based venture online, is shooting for a January bow to distrib music and film content on its first two channels. It would compete with RealNetworks and Broadcast.com.