Ken Rice confessed at a trial in Houston that he and ex-Enron boss Jeffrey Skilling and four others had inflated the division's capabilities.
Mr Skilling and the other defendants have all pleaded not guilty.
Former US energy giant Enron went bankrupt in December 2001 with massive debts.
The other defendants - former joint chief executive of Enron's broadband division Joseph Hirko, company vice-presidents Scott Yeager, Rex Shelby and Kevin Howard, senior accounting director Michael Krautz - also have pleaded not guilty.




