It may have something to do with your workspace layout. I know that 'Classic' layout restricts some of the choices you get in the Dreamweaver dialogue/cofiguration boxes.
Have a look in the Menu: Window > workspace Layout > and choose a different layout. See if you get the FileField options then.
Don'tworry about what the layout looks like - you can add or remove panels, and drag them to positions you feel comfortable with, then save the workspace by clicking 'New Workspace' and giving it a name.
Hope this works for you.