I just bought the game off Steam yesterday, and started playing today. I'm only a hour or so into the game.

A big annoyance I've come across is that some NPCs I talk to don't activate any voiced dialogue, and the subtitles for what they *would* have said skims by WAY too fast for me to read.

Any ideas?

I had that issue with shivering isles back in 07 (or 08??)
I just reloaded a save/restarted the game and it was gone.

Have you tried that?

I've tried reloading on several occassions, but it doesn't help. >_<

At this point, I'm reinstalling the game. WIth this dialogue bug, it's practically unplayable.

I had this exact same problem on another game that I was playing a while back (don't remember which one though lol). Anyways... If memory serves correctly, updating drivers resolved the issue. Not going to say this will definitely fix your issue, but always a good idea anyway.

Since i know this has happened with other games as well, you may trying doing some google researching to see what turns up. (I would help you out with that, but currently at work )