If you are not putting it over a video then you just create a text generated media. The background will appear black but it is actually transparent so that if you put video on a track below the text track you would see the text over the top of the video.
Write your text. Then go to track motion and set a keyframe with the text in the starting position (above the screen if you want). Then set a second keframe with the text at the bottom (on the ground :)) When you play this the text will move from the top to the bottom over the period of the keyframe. You want another text item ‘falling’ at the same time but at a different rate?? Make another generated text and place it on a separate track above the first and make it either longer or shorter than the first one. Then place keyframes in the track motion with the first one above the screen and the last one ‘on the ground (or below if you want)You just keep building this pyramid with as many text events as you want. Except if you have the ‘lite’ studio version of Vegas you are limited to 4 video tracks – the full version is basically unlimited.
If you have more questions I can email you a .veg file example to look at.