Maybe this code helps you.
Code:
Dim oneLine As String 'one line of the file
'open the file
Open "c:\myfile.txt" For Input As #1
    'read each line and add it to the textbox
    Do
        'read a line
        Line Input #1,oneLine
        'add it to the textbox
        Text1.Text = Text1.Text & oneLine & VBCRLF
    Loop Until Eof(1)
'close the file
Close #1