or vice versa... say if I have 10 list boxes and any one of them show the value as 'Positive', have that same 'Positive' value show up in another form field that started out blank
The first request is simple, if the target field is a text field: You simply need to calculation script to copy the value of the source field to the target field. Its' more complicated with a list box, as you need to add the new item to the list of current items, but it's doable.
The second request is possible, but a bit trickier: You will need to use a calculation script that iterates over all of the fields, and if any of them is set as "Positive", apply that value to the target field. If none of them are, apply a default value (blank or "Negative" or whatever).