Why not have 2 sets of list controls, a checkbox list for 1 and a radio button list for 2. If button 1 is selected, hide the radio button list and show checkbox list, else, the other way around.
[Edit]
OK, so 2 controls will not work. Try this then. Let me know if it works for you.
private void checkedListBox1_SelectedValueChanged(object sender, EventArgs e)
{
if (radioButton1.Checked)
{
for (int i = 0; i < checkedListBox1.Items.Count; i++)
{
checkedListBox1.SetItemCheckState(i, CheckState.Unchecked);
}
checkedListBox1.SetItemCheckState(checkedListBox1.SelectedIndex, CheckState.Checked);
}
}
[/Edit]