#Num! in Access2000 report

I have a created a report in Access 2000 that get data from our Unix acounts application using ODBC. Sometimes however the data is the value “0” in 2 boxes that are set to be divided by each other. This gives you the answer of #Num! in the calculated box. I have tried conditional formating and using Iif (Immediate If) to tell the box not the display if this in the answer, but have had no success as yet. Any clues!