So if they are definitely text files, which ones are they? The only ones in the
archive are SWFs, so I'm wondering if you're trying to load the character codes from the archive via the custom dialogue box (which will do absolutely nothing because they'd be the wrong format).
Anyway, if you've got dialogues from the Dialogue subforum it should just be a matter of clicking Load under Custom Dialogue, navigating to the file you downloaded and selecting it.