SQL Functions

I want fo format a numeric field as a string with leading zeroes

eg Format("PositiveNumberField", '000') in a query table, but the SQL gives an error on the above.

How can I do this ?

The reason i am having to do this is that I wish to display a number field in a summary report and it insisted on it being a group by field and not a value field. Am I taking the right approach or is there an alternative ?

Thanks