I just spent about half an our trying to get Flash to recognize a blank text field as 0.
First I wrote a function to strip out the blanks (maybe Flash already has this, but anyway...), but when I tried an if statement to check if the empty input box.text was == to empty (''), I kept getting false.
It turned out that the html option was on, so even an empty text input box has a sort of text associated with it, the html tags.
How irritating - but now I have switched off the html option, so it is just a plain old text box, and an empty space is just empty space.