In a high-profile trial that's expected to last two weeks, the $100 million case of Rosie O'Donnell vs. magazine publisher Gruner + Jahr (and the company's $125 million countersuit against O'Donnell) finally kicked off in Manhattan's New York Supreme Court on Thursday.

And the fireworks quickly followed, as a lawyer for G + J claimed in opening statements that the 41-year-old star was "vindictive" and "had a foul-mouthed temper tantrum" when working on their now-defunct joint venture, Rosie magazine.

The publisher claims O'Donnell acted unprofessionally and breached her contract by killing the magazine in September 2002. She, in turn, is charging that G + J damaged the name and reputation she has built up over 20 years because the publisher exerted editorial influence that contradicted her decisions.

The case is being played out before a judge, without a jury, and O'Donnell herself is expected to testify.

In the opening statement, G + J's lawyer said the 41-year-old star threw a fit while discussing contents of the September 2002 issue with newly hired editor Susan Toepfer (a veteran editor from PEOPLE). O'Donnell also reportedly told Toepfer that the cover photo she picked made Rosie look "f------ fat."

"She is a celebrity, vindictive and usually gets her way, and surrounds herself with people who would placate her," according to the opening argument, as quoted by CNN. "She didn't have the right to abandon the joint venture."

Outside the courthouse Thursday morning, O'Donnell (who also had been making noises about using her court appearance to publicize the new $10 million Broadway musical "Taboo" that she is producing) reiterated to reporters that she was fighting to clear her name.

"Every person as successful as me (sic) has the reputation of being difficult, especially if you're a woman," said O'Donnell. "It's funny to me that I'm going to court for this. It's hysterical to me."

O'Donnell added: "We had a business deal; it went wrong." Later, she said, she was so nervous about having to come to court that she threw up, according to New York's Daily News. (The Post reports she threw up in the judge's chambers during a break in the session.)

In her opening statement, O'Donnell's lawyer, Lorna Schofield, said G + J had assured her client of editorial control, and that there was a breach of that contract.

The attorney added that O'Donnell had invested $6 million of her own money in the magazine.