Dim my_string As String = vbTab & "row1  " & vbNewLine & "" & vbTab & "  row2  "
Dim rows As String() = my_string.Split(vbNewLine)
Dim text As StringBuilder = New StringBuilder
For Each row In rows
    Dim trimmed_row As String = row.Trim()
    text.Append(trimmed_row.ToString() & vbNewLine)
Next
Response.Write(text.ToString())
Or with Linq:
Dim trimmed_text = String.Join(vbLf, my_string.Split(vbLf).[Select](Function(s) s.Trim()))