Changing the behaviour of DataSource property of combobox

I'm trying to change the behaviour of setting the DataSource property
of combobox.

I was told on this list to override the ToString() function, but i
don't think this works or I'm doing it wrong.

Here is the behaviour I now see.

Setting the DataSource property of combobox to an ArrayList will visual
display
the first value in the Text field. ( or setting the Text property ).

I don't want this to happen. Just load the DataSource, don't change the
Text property.

Any Ideas