There is probably an elegent solution but this should work in the interim:
Right click on the field and select format field
Click on teh NUmbers tab
Click on Customize
Click on the formula next to Decimals
add this formula:
if right(totext({table.numberfield},4),4)="0000" then 0 else
if right(totext({table.numberfield},4),3)="000" then 1 else
if right(totext({table.numberfield},4),2)="00" then 2 else
if right(totext({table.numberfield},4),1)="0" then 3 else 4