How do I do handle client side validation in JSP pages that use JavaBeans and scriptlets? In particular, I'd like to unhide or display other fields/options depending on the user's actions on previous fields.

One way to do it is to use div tags. Form groups of elements and put them within seperate divs. You make these individual div visible or invisible based on your conditions and can also position the divs around on the screen by changing their x and y co-ordinates. I tend to use JavaScript to achieve Client-side validations.