VS 2010 : Storing Data In Txt File For Program Use?

In the program I'm working on, there is a 'sign-in' form that pops up for the user to enter first name, last name, and DOB. What I want to do is STORE that information in a text file for FUTURE use by the program (i.e. displaying a list of all previous users of the program).I already know how to use streamwriter to write text to a file, but I would like for the text file to be stored within the program files and also for a new user's data to be appended to that file every time.

Do I simply add the text file to the project files? When I do that, its path is 'My Documents'. How will that affect the program when I publish it? I guess I just don't yet understand what happens when the program is finished and published. The code for the 'Submit' button on the sign-in form is pasted below. At the bottom, I've put a comment to indicate where I want to store the data to a file.

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim TxtBox() As String = {TextBox1.Text, TextBox2.Text, TextBox3.Text}
For i As Integer = 0 To 2
If TxtBox(i) = Nothing Then

[code]....