Rod - the answer is different depending on whether the data has been typed a numeric field, or text field i.e. ID numbers. If text, in DataExplorer tabs, you could use the Table View Tools > Tools > Append/prepend values and specify a prepend of a '0'. As you discovered, you can also also write a simple formula: [Padded] = 0+[Unpadded] and this will prepend "0" in text. One advantage of writing a formula would be that you can move the operation 'upstream' to DataManager by adding this formula field into a Field Organiser block where the operation is more visible and manageable if your inputs change.
If the field is numeric, you can not currrently prepend a zero...only manage the decimal places to the right of the decimal.