no carmen diaz wasn't in that movie it's Malin Akerman your talking about
Mali Akerman plays the sister
and Katherine Heigl is the sister in love with the boss george which her sister steals him from her
the movie is called 27 dresses
http://en.wikipedia.org/wiki/27_Dresses
http://www.27dressesthemovie.com/
http://www.imdb.com/title/tt0988595/
Two things about Jane: she never says no to her friends (she's been a bridesmaid 27 times and selflessly plans friends' weddings), and she's in love with her boss, George, nurturing dreams of a lovely, romantic wedding of her own. She meets Kevin, a cynical writer who finds her attractive, and that same week her flirtatious younger sister Tess comes to town. Jane silently watches George fall for Tess, a manipulative pretender. Worse, Jane may be called upon to plan their wedding. Meanwhile, Kevin tries to get Jane's attention and has an idea that may advance his career. Can Jane uncork her feelings
Jane is career-oriented and secretly in love with her employer, George. She spends much of her time as a bridesmaid, and has 27 dresses as evidence. Then her structured and ordered life comes unhinged when her younger sister, Tess, re-enters her life, and a reporter, Kevin, is attracted to her. Kevin decides to publish Jane's secret and her overwhelming wardrobe. Things get even more complicated when Jane finds out she may end up losing George to none other than her very own sister
http://en.wikipedia.org/wiki/27_Dresses
Jane Nichols (Katherine Heigl) has been a bridesmaid for 27 weddings. One night when she is attending two weddings almost simultaneously, she meets Kevin Doyle (James Marsden), who helps her home but repulses her with his cynical views of marriage and finds the planner she left behind in the taxi they shared.
Meanwhile, Jane's younger sister Tess (Malin Akerman) comes home to visit for a couple of weeks and falls in love with Jane's boss George (Edward Burns). Tess pretends to like the same things George does so that she can get him to like her; despite loving George herself, Jane does not reveal the truth and the courtship progresses rapidly. Soon the new couple announce that they intend to marry in only three weeks. Jane's and Tess's father gives Tess their mother's wedding dress to wear, even though Jane had always wanted to wear it to her own wedding. The reporter who agrees to cover their wedding for the society page turns out to be Kevin, who writes wedding announcements under a pseudonym: Malcolm Doyle. The reason he didn't return Jane's planner, after finding it, was so he could gather material for a piece on the "perennial bridesmaid" and hopefully be promoted to writing investigative pieces about "real" news.
Jane is unaware of Kevin's intentions and, when he asks to interview her for his column on Tess, gets her to try on all 27 bridesmaids dresses in her closet. He takes pictures of her in all of them and sends the completed article to his boss. As they get to know each other because of Tess's wedding, Kevin begins to think that Jane is not as one-dimensional as he thought, and asks his editor to hold his article so he can "fix" it.
Jane becomes increasingly uncomfortable with the fact that Tess still hasn't been honest with George. She almost tells George the truth about her sister when Tess is away and Jane is helping him choose dinner for the reception. Kevin walks in on the meal and realizes that Jane is in love with George and can't understand how she can go on planning her sister's wedding. Kevin and Jane drive to Rhinebeck to pick up linens for the wedding, they get stuck in a rain storm and eventually so does their car. After they seek shelter at a bar, they get drunk and sing "Bennie and the Jets". After finishing their song, they share their first kiss they have sex in Jane's car.
The next day, Kevin's article is published along with all the pictures of Jane in her dresses, leaving her hurt and embarrassed. Upon getting back to the city, she must also deal with an enraged Tess whom Kevin had portrayed (somewhat correctly) as a bridezilla. To save face, Tess writes a script of what she wants Jane to say along with the slide-show to be shown at the rehearsal dinner. Jane is horrified when she finds out that Tess had their mother's wedding dress cut up to make it look more fashionable. At the rehearsal dinner, Jane says what Tess wants but fills the slide-show with pictures depicting the real Tess, and George finally learns that Tess isn't who he thought she was. The wedding is called off and Jane sees Kevin as she leaves the dinner. He gives her a BlackBerry to replace her Filofax, telling Jane that he was happy she finally stood up for herself and, though she is mad at him about the article, he just wanted to come to the dinner and be there for her.
Later at work, George tells Jane that he appreciates her because she never says no. Remembering that Kevin once said the same thing as a criticism, Jane quits and admits she only stayed at the job because she was in love with George. She discovers after an experimental kiss that she no longer loves him and decides to meet Kevin. She announces in front of the entire crowd at a wedding that he is covering that she is in love with him. Kevin then kisses Jane.
One year later, Jane puts on her 28th dress — her wedding dress and marries Kevin. George and Tess meet again since breaking up, and Tess reintroduces herself, being completely honest this time. Tess and Casey (Judy Greer), Jane's best friend, are her maids of honor. All 27 brides Jane has been a bridesmaid for are bridesmaids for her, each wearing the dress Jane had worn in their weddings.