C#

-Nick Parker
DeveloperNotes.com

protected override OnClick(EventArgs e)
{
  if (this.Parent == null) return;
  foreach (Control c in this.Parent.Controls)
    if (c is RadioLabel && ((RadioLabel)c).Group == this.Group)
      // Easy-to-property like RadioButtons have, and also draws or remove
      // the border like A.Wegierski mentioned (if you did it that way).
      ((RadioLabel)c).Selected = c == this;
}

public GroupCollection Group
{
  get { return this.group; }
  set
  {
    // Remove this control from the group, even if null is assigned
    // (easy way to remove a RadioLabel (or whatever) from its group).
    if (this.group != null) this.group.Remove(this);
    // Assign the group and, if not null, add this control to it.
    this.group = value;
    if (this.group != null) this.group.Add(this);
  }
}

private TabPage GetTabPageFromPoint(Point p)
{
  // If the X and Y coordinates from the drag-drop operation are still in
  // screen coordinates, don't forget to translate them:
  p = this.tabControl1.PointToClient(p);
  for (int i=0; i<this.tabControl1.TabPages; i++)
  {
    Rectangle rect = this.tabControl1.GetTabRect(i);
    if (rect.Contains(p)) return this.tabControl1.TabPages[i];
  }
  return null;
}