I used both Near Infinity and DLTCEP for this and though I managed to familiarize myself with the DLG editor in them
That was largely a waste of time.
when I went into the game my NPC did not once respond even though I had assigned the dialogue to them via DLTCEP. A quick test showed me that when I switched the dialogue with one from the game I'm trying to mod (IWD) that the NPC did respond. Now would this have anything to do with me putting the DLG files in the OVERRIDE folder? According to quite a few tutorials I have been reading it was suggested to do that for testing purposes.
Any new files you create will inevitable end up in override (or, somewhat less likely, in a BIFF file, but it's really not worth doing so in 99% of cases.)
Presuming you actually did create a DLG file, populated its strings, and placed the DLG in the override, the most likely cause of "no talking" was that there were no valid state triggers (such as True(), always a safe one for getting your feet wet since it should always work.)
However, I exhort you to learn how to use WeiDU for dialogue creation. Not only is it vastly superior to the graphical editors, but then you can share your source code and get it corrected, rather than trying to describe how you made the DLG file in a graphical editor, which usually doesn't end well.