Click the first line of text in the scroll to select it. The click the "Styles" tab (next to "Properties) and select the justification you want.
The only "gotcha" is that ALL paragraph text will have this justification whether you want it to or not :-(
Create your text in a paint program that DOES allow justified text. Save that as a picture - preferably with an alpha channel. Import that into Vegas and use Pan/Crop to scroll across the text.
Thanks. Been there, done that but was hoping that there was a secret "built in" way of accomplishing this in Vegas, especially for "text editing" purposes.
You could try the Graffiti add-on provided with Vegas 5 (or the full version of Red). Or the new tool by Cayman Graphics. Or Bluff Titler or Cool 3D or Heroglyph...