Hey, complete noob at quest designing here.

I made a dialog from the Creation Kit Quest Tutorial, but as soon as the actor replies the dialog skips to the next line... completely randomly!!

That's a common issue, rite... How can I fix?

I don't use voice acting of any kind.

Since the dialogue does not need to wait for a sound clip before moving on, it goes through as fast as the computer can read the display lines, not as slow as we can. This will require adding some blank noise for as long as you want the text to display.

This is shown in this tutorial:
http://www.creationkit.com/Bethesda_Tutorial_Dialogue

With the head "Recording a Temp Track" (without quotes).