VS 2012 - Dynamic Text Boxes Based On Textbox Number Entry

I'm going to have a textbox on my ASPX page - where users can enter a number between 1-50.

Based on their selection, I'd like to add three textboxes for each number and number them appropriately.

I'd like three textboxes for each "number", so for example, the fields would be:

Name1, PIN1, Desc1
Name2, Pin2, Desc2
Name3, Pin3, Desc3
...

So, how do I, at runtime, add these fields to my page?

Secondly, This form, upon submittal, creates a configuration file on my server currently in the format of

[FIELD1]
FieldOne.Value
[/FIELD1]

[FIELD2]
FieldTwo.Value
[/FIELD2]

[FIELD3]
FieldThree.Value
[/FIELD3]

With those fields, it's rather easy, as the form has static controls that I'm looking up and sending to my file.

How would I add the dynamic controls to the file as well? Obviously, if they've selected to add 10 fields, I don't want 40 other fields of blank/nothing (since they can choose to add up to fifty). How would I iterate only adding the fields that they've chosen?

I'm writing in VB.NET not C