After effects has a plugin that can do the old 3-D effect. I have never used it so you may want to post the same question on the After Effecs board. I don’t know if there is some sort of long work around you could do in Vegas to achieve this effect.
Did you shoot the film in 3D (ie: with 2 cameras side by side about 2 1/2 inches apart)?
Vegas can certainly create the elements for Anaglyph (red/cyan) 3D within the program if the original camera material is shot in 3D.