Try this in the 'Display String' formula for the field. The formula uses compares the number against the integer part of the value to figure out whether to include the decimal point and 2 decimal places.
It works in Crystal 10, but I can't remember if you have 'Display String' formulas in Crystal 9:
If Int(CurrentFieldValue) = CurrentFieldValue then
ToText (CurrentFieldValue, 0)
ToText (CurrentFieldValue, 2)