I find the easiest way to do it is with random numbers. You have two possible outcomes, so make a random number generate either the number 1 or the number 2. Then depending on that random number, assign a certain text to the textbox.
I.e
[php] Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Dim RandomClass As New Random()
Dim i As Integer
i = RandomClass.Next(1, 3) 'this will make 'i' either 1 or 2.'
If i = Val(1) Then
TextBox1.Text = "I iz pro"
Else : TextBox1.Text = "I iz newb"
End If
End Sub[/php]
Hope that's what you were asking for :P