in answer to the first part:
=IIf(OR([data1]="",[data1] is null,[data2]="",[data2] is null)=True,"0.00",[data1]+[data2])
Something like that in the control source hopefully might do the trick...
Or just
=IIF([data] is null,"",[data])
or
=IIF(isnull([data]),"",[data])
Not sur eif the last two would work properly...
HOpe it's of some use!
Aubs