Sean,
Without some sort of VBA to interupt the print and update
numbers (I don't even no if that could be done) your will
have to opt for a different approach.
First question, do you have to use text boxes? If you
could use a table it would be simply a matter of
performing a mail merge to lables. See:
http://www.gmayor.dsl.pipex.com/Numbered_labels.htm
If you have to use Text Boxes and since Text Boxes will
not accept "Next Record" merge fields, you will have to
alter your Data Source. This is pretty easy using the
Excel method that Graham discusses in his article above.
In testing this out, I created eight columns named First,
Second, etc.
The first column was numbered 1,9,17...393, etc. the
second 2,10, 18...394 etc. and so on. Basically you have
a 8 by 50 source containing every number 1-400
Now you can insert the mergefield named First in one Text
Box, the field named Second in the next box and so on.
When you merge, you get a fifty page document that when
printed will give you 400 numbered text boxes.