Adding a combo box in an Excel cell

[Sathyaish]

How do I add a drop-down list/combo box to a column in an excel worksheet? I wish to add an editable combo box in one of the columns of an excel worksheet so that the user could either type in some text or choose from the list of entries in the combo box. In another column, I wish to add a non-editable combo box/list box wherein the user can only choose from the list and not write anything else which is not there in the list. I am not very familiar with VBA.