I had a similar problem a few months ago. You might want to check it out. I used HUGE PSD and TIF files in my timeline with up to 4000 px. The computer kept crashing when rendering. So i scaled down the images to about 2500 px or 3000 px. Then saved them as high quality JPG. That solved my problem.
Does anyone have experience with P2 DVCPRO HD? on vegas? I have a tool converting the HD clips to AVI and QTmovie, but i need a fast computer that can handle real hd with a good workflow, hopefully with a black magic design card. Any specs?