txt file help



ok i am editing a text file line by line, i have it so i can view each line in its own text field with a submit button for each line and all that happy stuff BUT! i don't know how to open a txt file, automatically go to a specific line, then only write to that one line without changing anything else.
i love when 4 letters (if a person is in a good mood then even only 3 letters) help people to figure out everything :D

For those of you that still dont get it: im talking about RTFM and RTM
no actually i went to another form and someone gave me a link to a tutorial that explained how it was done and how everything worked so i understood what i was doing. http://codewalkers.com/tutorials/57/9.html is the tutorial if anyone else was having the same problem as me. :-D