How could I possibly turn Fallout 2's dialogue audios into a more usable form?
And, well, where to locate them?

I'm not sure about the audio, but the Dialogue (text) files are available on the vault.

Yes and texts in game files can be opened with Notepad.
But I'd like to use the audios too.

You can find the files in the FO2 master.dat they are in an ACM format, which you will need to convert to wave:

ACM tools
http://www.nma-fallout.com/forum/dload.php?action=category&cat_id=29

Dat Tools
http://www.nma-fallout.com/forum/dload.php?action=category&cat_id=27

Note about the tools...
IIRC, ACM2WAV has a commandline ( -m ??? maybe ???) that treats the audio as mono instead of stereo (like the music tracks). If you convert the voice as stereo you get Chipmunks (which most likely won't be what you want)