If it's a certain script you're after, then you open up the Sourced script with KotoR tool (or extract it and open it up with notepad). You'll find the contents of the script in there. Alternatively, if you just want the already compiled script, extract the Compiled one you want. Now open up your chosen dialog file with the DLGEditor and click on any any entry you want (mainly the one you want to fire the script). You will find a few boxes on the bottom, one says "Script that fires when spoken" and add the name of your Compiled script (without the extension!). Now press File>Save and then drag the dialog file and the script into your Override folder in your KotoR directory.
From what I gathered, that was what you were after. Now I know that it's a really big headache when it comes to modding, but if I got your problem wrong, try and explain what you want to happen and I will guide you through it best I can. Also, you can try posting your particular problem in the modding section, Holowan Laboratories:
http://www.lucasforums.com/forumdisplay.php?f=324)
Good luck!