le differenze tra vb6 e vb.net sono tante...inoltre l'accesso ai file è completamente diverso quindi ti posto del codice d'esempio
Scrittura
codice:
Imports System
Imports System.IO

Class Test
    Public Shared Sub Main()
        ' Create an instance of StreamWriter to write text to a file.
        Dim sw As StreamWriter = New StreamWriter("TestFile.txt")
        ' Add some text to the file.
        sw.Write("This is the ")
        sw.WriteLine("header for the file.")
        sw.WriteLine("-------------------")
        ' Arbitrary objects can also be written to the file.
        sw.Write("The date is: ")
        sw.WriteLine(DateTime.Now)
        sw.Close()
    End Sub
End Class
Lettura
codice:
Imports System
Imports System.IO

Class Test
    Public Shared Sub Main()
        Try
            ' Create an instance of StreamReader to read from a file.
            Dim sr As StreamReader = New StreamReader("TestFile.txt")
            Dim line As String
            ' Read and display the lines from the file until the end 
            ' of the file is reached.
            Do
                line = sr.ReadLine()
                Console.WriteLine(Line)
            Loop Until line Is Nothing
            sr.Close()
        Catch E As Exception
            ' Let the user know what went wrong.
            Console.WriteLine("The file could not be read:")
            Console.WriteLine(E.Message)
        End Try
    End Sub
End Class
bye