Something like this should work
Dim f As Integer
f = FreeFile
Open "c:\temp\myFile.txt" For Input As #f
Dim col As Integer, row As Integer
col = 1
row = 1
Dim text_to_enter As String
Do Until EOF(f)
Input #f, text_to_enter
MSFlexGrid1.TextMatrix(row, col) = text_to_enter
row = row + 1
Loop
Close #f
Warning - I don't have VB6 any more so I haven't been able to test this
Some references that might help:
Using the FlexGrid control[
^]
Reading Simple Text Files[
^]