In layout mode, select the field and then specify its format on the Data Formatting section of the Inspector's data tab. If you specify currency for the data format, you'll see a box appear where you can specify what decimal separator to use for this field.
It depends upon why you want this - I am not clear to the reason.
If it is just display, then you can set the decimal to comma on the layout (Inspector > Data > Data Formatting at the bottom and then down under Separators.
If this should affect the data itself then you will need to handle it at the OS level. To change an existing file, you will need to create an empty clone on the system with the OS set to comma instead of decimal. Then you would need to import your data into it.
it'n not only a layout problem, the number need for a paypal transaction.
I solved the problem with a script :
1. $1 = lenght(number)
2. $int = int(number)
3. $2 = lenght($int)
4. $3= $1 - $2
5. if $3 = 0 -> $dec = 00
if $3 = 2 -> $dec = right (number,1)
if $3 = 3 -> $dec = right (number,2)
6. $correctnumber = $int & "." & $dec
strange but works!!