OK, we've got a workaround for this problem, but it's not perfect yet. If you wish to try it out, please download the archive found here and unpack it into Sanitarium's folder (thus replacing the current sntrm.exe file with the one you downloaded). The "not perfect" part means that the game works great only until you change chapters.
This means there will be no problems when:
1) You launch the game and start a new game,
2) You launch the game, load chapter A and play it.
But all dialogue lines will be skipped if you load a different chapter:
1) When you play chapter A and load chapter B from a saved game,
2) When you finish chapter A and progress to chapter B.
To get around this, you need to save the game at the start of each new chapter, close it (Alt-F4 to make it quick), restart it and load the saved game. We'll see if we can come up with a version with this problem fixed. Until then please use this temporary fix if you wish to enjoy the "talkie" dialogue lines.