I'd use a script.
Have a trigger with the following code in it's
condition field:
resistanceguy distance player < 10
and in the
on activation field type something like
this exec "conversation.sqs"
Now, the trigger will fire when the resistance guy gets within 5 meters of you - you can change this to suit your needs.
Now, I'll assume you know how to use scripts, so here's the basic setup you'll need....
;conversation.sqs
titletext ["Hi.","plain down"]
~5
titletext["Back atcha.","plain down"]
exit
This will splash the text on the bottom of the screen. "Plain down" will place it at the bottom of the screen - there are other things you can substitute in this place but for your purposes that will work fine.
~5 is the command to wait five seconds before proceeding. Change the number accordingly so that you can read everything that's up there before the next line of text is displayed.
\n will put in a line break, which is useful because if it's a really long piece of text, it will just run off the sides of the screen.
*EDIT* this is only necessary if you want a back-and-forth conversation. If you only need him to say something you can do in one line, forget about the script and go into the "Effects" section of the trigger itself and put in the text there.