Hi Patrick Thanks for your reply!
I didn't find where to set a field's locale in the Format options. But i solved my problem, i changed the Form language in the Form Options and set it to Spanish (United States). Now it recognizes the dot as decimal mark at least, but all the other languages where the comma is the decimal marks it doesn't :S
Another Question: Is there a way to change the keypress, so if the user presses "," it will automatically change to "." so the form will do the right calculation. Because now, if the users presses "," it ignores it automatically and if the user don't realize this automatic change... It will calculate everything wrong.