Use body field for views nivo slider instead of title field
When you set up the view, you can click on the Row Style options (the little gear thingy :) and then it will give you three options, Image Field, Title Field, and Link Field.  The Title Field is the Caption and you can put any field that you've selected in your view (in Fields) you want for it. So, if you've selected Node Body as a field, you should be able to select it there.  But, just as using the Node Title, it will put in the whole body (or at least what part will fit I'd imagine) in the caption.  If you want something else, you may want to consider yet another field in your content type, or some sort of views rewriting of the field.