Entertainment Weekly has dismissed the rumors that Vanessa Hudgens (High School Musical films) auditioned for a role in the Twilight sequel, New Moon:

Sources inside Summit Entertainment and Hudgens' camp tell EW that the filmmakers aren't looking at the star (best known as High School Musical's Gabriella Montez) for any role in the soon-to-be-shooting Twilight followup.
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So far confirmed for the next installment are Kristen Stewart, Robert Pattinson, and Taylor Lautner as well as director Chris Weitz. New Moon will open in theaters November 20th, 2009.