It all depends on the layout of your .dat file for one.
If you just mean find the two smallest values and there is one number on each line, you could just have two variables (small_1, small_2) and check each line to see if it's smaller.
if your file looks like this:
1) Set small_1 & small_2 to maximum size (65535 for WORD)
2) Check for end of file, if eof, goto 7)
3) Read number (n) from file
4) if n < small_1, set small_1 to n and goto 2)
5) if n < small_2, set small_2 to n and goto 2)
6) goto 2)
7) show small_1 & small_2