Julia, that's a heplock, what you're talking about.
You don't have to have an iv if you're planning a non medicated birth, but, as a previous poster mentioned, you might face a fight with the hospital staff. Make sure that your labor support person (husband, partner, etc) knows what you want and don't want, so that he/she can fight on your behalf, if necessary. If you don't feel your support person will be up for that, you might consider getting a doula.
Hope this helps!