ComboBox suitable event..need help

Question

Hello to all fellows,

i have a combobox binded with a column of a datatable.The size of combo is not suitable according to record size(Design requirement,hope u understand).i just want to know that whether is there any suitable event which i can use while opening combo and placing mouse pointer on it,i can get a tool tip text.Although i have used tool tip text after selection of value (when the Combo_selected_index has been fired and combo is given value) but it seems better as the user moves pointer on combo's records the tool tip also starts working?

Any Ideas???