Dresses were generally one-piece garments from 1800 through the 1840s; after that it became common for a dress to be made as a separate skirt and bodice, and many dresses had a "day" bodice with a high neckline and long sleeves, and an "evening" bodice with a low neckline (decollete) and very short sleeves. Dresses however can be cooler and less confining than many trouser styles, and they are still very popular for special occasions such as proms or weddings. Dressing conservatively is always the safest route, but you should also try and do a little investigating of your prospective employer so that what you wear to the interview makes you look as though you fit in with the organization.