The main idea is that you must first identify the data source for each one
for grid view and details view
then the code that you want is 


+++++++++++++++++++++++++++++++++++++++++
protected void resultGrid_SelectedIndexChanged(object sender, EventArgs e)
    {
        SqlDataSource1.FilterExpression = "QuestionOrder=" + resultGrid.SelectedValue;
    }
+++++++++++++++++++++++++++++++++++++++++


on this code you have to assign the data sourse(sqldatasource1 on this example)
which is a data source for details view to the row selcted from the grid view(resultgrid on this example)

Note: there is a relation between these tow sources on the (questionorder field)



I hope that is clear to you..

Good luck..

Am0nah