There are HTML attributes that can generate tool tips. I believe the "title" attribute on an <a> tag will create a tooltip.
If you make the hidden field not visible at the server side, it won't render. I can't imagine why one would do this however, as the hidden field is, well..., already hidden.
You could change the description field into a template column, put a hidden relative position div with the complete description and show it when you mouse over the truncated value.