Here is a rought translation to .NET although you could use the Compatiblity namespace to use almost the same code you have there.
VB Code:
  1. Dim filepath As String = "C:\Code\Practice\TestBed9\bin\grades.txt"
  2.  
  3.         'create arrays (or in this case arraylists)
  4.         Dim labs As New ArrayList
  5.         Dim questions As New ArrayList
  6.         Dim tests As New ArrayList
  7.         Dim participations As New ArrayList
  8.  
  9.         'open file
  10.         Dim fs As New IO.FileStream(filepath, FileMode.Open)
  11.         'create reader for file
  12.         Dim sr As New IO.StreamReader(fs)
  13.         'read until there is no more to read
  14.         Do While sr.Peek > -1
  15.             'read one line at a time
  16.             Dim line As String = sr.ReadLine
  17.             'parse into fields
  18.             Dim fields() As String = line.Split(Char.Parse(","))
  19.             'test for student match
  20.             If fields(0) = cboStudent.Text Then 'name
  21.                 Select Case fields(1) 'type
  22.                     Case "Lab"
  23.                         labs.Add(fields(2)) 'grade
  24.  
  25.                     Case "Questions"
  26.                         questions.Add(fields(2)) 'grade
  27.  
  28.                     Case "Tests"
  29.                         tests.Add(fields(2)) 'grade
  30.  
  31.                     Case "Participation"
  32.                         participations.Add(fields(2)) 'grade
  33.  
  34.                 End Select
  35.             End If
  36.  
  37.         Loop
  38.         'close and release file
  39.         fs.Close()

Also there could be a number of improvements if you wanted to go OOP with it. You could then make a Grades or Student class/collection and just serialize/deserialize it to and from disc. Then there is no parsing required and you can keep the data in memory for faster access.