Nicole Richie is desperate to marry as soon as possible.'The Simple Life' star, who is four months pregnant, is said to be determined to wed boyfriend Good Charlotte Joel Madden before her baby bump shows. A source told E! Online: "Nicole does not want wedding pictures of her in a big old white dress, with a big old pregnant belly."The 25-year-old star wants a lavish wedding, but is struggling to set a date to exchange vows before September 28 - when she must begin her four-day prison sentence for DUI (driving under the influence).The source added: "Nicole has a guest list of about 200 so far. But pulling off a wedding that size, this quickly isn't easy. She really wants to get married, spend a few days with her new husband and then check in to jail."Nicole's father, singer Lionel Richie, has offered his Bel-Air mansion for the wedding ceremony and Nicole is said to love the idea of getting married at home.It was revealed earlier this month the couple are having a baby boy and Nicole has already started decorating the nursery and choosing names.