Note: this is added in here, because it's sometimes overlooked by new users.
Auto-scrolling is an option available at the top of the Speech Manager. From there you can also adjust the scrolling speed. If you are not going to be using actual voice clips, you may take a look at the Subtitle-Scrolling audio option which can be found both in the speech manager and in each Player/NPC. This can be used to set "beeping" voices, in the style of older games (and some modern JRPGs, etc), it can also be used to create Typewriter sound FXs, etc.
If you want the scrolling to stop at certain points, you can use the [wait:X] token within your speech text - where "X" is the duration of the wait in seconds. See Section 10.4 of the Manual for more information.
If you'd like to go further, you can use custom scripting to trigger events when speech is played - see this tutorial. With the OnStartSpeech event, you can add extra functionality when speech plays - or even override AC's display of it entirely.
-Original tip was provided by ChrisIceBox. Edited by Alverik-