Should this be conditional on what's being entered into the first box? Also, should the second box be otherwise editable?
It should just be any time data is entered into text box 1. Text box 2 can be otherwise editable yes. Thanks.
You can use something like this is the first field's custom validation script:
if (event.value!="") this.getField("Text box 2").value = "00";
Adjust the field name if it's not identical to the one in your file, of course.
That seems to do the trick. Thanks so much. You're the best.