[mrcnn]

Если массив текстбоков

Dim st As String
st=""
For i = 0 To aSz - 1
st = st & aTx(i).Text & " "
Next

В случае необходимости Cstr

а дальше супер стандартная запись
Dim fs As IO.FileStream, sr As IO.StreamReader
Dim FileName As String, sw As IO.StreamWriter
SaveFileDialog1.ShowDialog()
FileName = SaveFileDialog1.FileName
fs = IO.File.Open(FileName, IO.FileMode.OpenOrCreate)
sw = New IO.StreamWriter(fs)
sw.WriteLine(st)
sw.Close()
fs.Close()

В проект добавить нуно SaveFileDialog1