Read Line-By-Line without using StreamReader - vb.net

Question

I have been doing A-Level Computing for a couple of months now and I have decided to make a phonebook relevant to the methods used in class. For my exam I am not allowed to use StreamReader etc... However, I can use methods such as FileOpen(1, "FILE NAME", OpenMode.Binary).
I want to store usernames and passwords in a text file (I know its not a good method but it links to my lessons). My .txt file is formatted like:
Username, Password.
Username2, Password2.
What would i be able to do to make it store each Username and Password in a list?
Here's what I've got... (don't know why it doesn't work)
Private Sub CheckAccount()
Dim Username_File As New ArrayList
Dim Username_Temp As String = ""
Dim Password_File As New ArrayList
Dim Password_Temp As String = ""
FileOpen(1, "Users.txt", OpenMode.Binary)
Do While Not EOF(1)
Dim PosCount_Start As Integer = 0
Dim PosCount_End As Integer = 0
Dim TempChar As Char = ""
Do
FileGet(1, TempChar)
If TempChar = "," Then Exit Do
Username_Temp = Username_Temp + TempChar
PosCount_End = PosCount_End + 1
Loop
Username_Temp = Username_Temp.Substring(PosCount_Start, (PosCount_End - PosCount_Start))
Username_File.Add(Username_Temp)
PosCount_End = 0
Do
FileGet(1, TempChar)
If TempChar = "." Then Exit Do
Password_Temp = Password_Temp + TempChar
PosCount_End = PosCount_End + 1
Loop
Password_Temp = Password_Temp.Substring(0, PosCount_End)
Password_Temp = Password_Temp.Trim
Password_File.Add(Password_Temp)
PosCount_End = 0
Loop
FileClose(1)
For i = 0 To Username_File.Count - 1
Dim Temp As String
Temp = Username_File(i)
If Temp.ToLower = Username.ToLower Then
If Password = Password_File(i) Then
LoggedIn = True
End If
End If
Next
End Sub