Version: Sony Vegas Pro Version 8.0

I have been trying to render a movie using various file types (mp1eg, mpges2, avi) but keep getting the problem of my video clips appear blank. The inserted text media and jpegs appear fine but when a video appears the screen goes black.

What is strange is that when I have rendered using mpeg1 on Video Rendering Quality: Preview and on low video quality it wqorked but the resulting movie quality is to oow.

The imported media clips that fail are avi's (xvid video compression).