how can i change the position of an item in the list box in c#.net with asp.net2.0?

[app98]

I am preparing a listbox it contains some items and it has two buttons ( up button and down button), when i pressed down button item was changing its position from up to down , but when iam pressing the up button it is not moving ????..this is my prob what to do pls make me clear.......... iam doing it in c#.net with asp.net2.0

[Arnon Mathias]

private void button2_Click(object sender, System.EventArgs e)
{
//// UP
if (listBox1.SelectedIndex >0)
{
String Temp = listBox1.Items[listBox1.SelectedIndex].ToString();
listBox1.Items[listBox1.SelectedIndex] = listBox1.Items[listBox1.SelectedIndex-1];
listBox1.Items[listBox1.SelectedIndex-1] = Temp;
listBox1.SelectedIndex--; // folow up by placing the selection again
}
}

private void button3_Click(object sender, System.EventArgs e)
{
if (listBox1.SelectedIndex < listBox1.Items.Count-1)
{
String Temp = listBox1.Items[listBox1.SelectedIndex].ToString();
listBox1.Items[listBox1.SelectedIndex] = listBox1.Items[listBox1.SelectedIndex+1];
listBox1.Items[listBox1.SelectedIndex+1] = Temp;
listBox1.SelectedIndex++; // folow up by placing the selection again
}
}