//Marks all checkboxes on a form as checked.
function CheckAllBoxes()
{
    var inputFields = document.getElementsByTagName("input");
    var field;
    var alreadyCheckedCount = 0;
    var checkedThisTime = 0;
    
    for(i = 0; i < inputFields.length; i++)
    {
        field = inputFields[i];
        if(field.type == 'checkbox') {
            if (field.checked == true) {
                alreadyCheckedCount++;
            }
            field.checked = true;
            checkedThisTime++;
        }
    }
    if (checkedThisTime == alreadyCheckedCount) {
        UncheckAllBoxes();
    }
    return false;
}

function UncheckAllBoxes() {
    var inputFields = document.getElementsByTagName("input");
    var field;
    var alreadyCheckedCount = 0;

    for (i = 0; i < inputFields.length; i++) {
        field = inputFields[i];
        if (field.type == 'checkbox') {
            field.checked = false;
        }
    }
}