How do I implement an owner drawn combobox

You can subclass ComboBox. In your derived class, make sure you set

  this.DrawMode = System.Windows.Forms.DrawMode.OwnerDrawFixed;
  this.DropDownStyle = ComboBoxStyle.DropDownList;

You also need to handle the DrawItem event to actually implement the drawing. Check out the details in the OwnerDrawnComboBox sample.