problems fading to black

Hope this is okay. I have used my Real Name now!!

Fading to black is resulting in poor quality with horizontal bands through it on the final DVD. The rest is fine. This happens with various authoring programs, so it must be a Premier problem. I have tried using a black JPEG (as opposed to fading to transparency) but still the same result. I am rendering to avi files which go into the authoring program. Funny thing, though, when I make a disc direct from premier it is fine. Trouble is, usually I want menus so I cant do this often, it was just that the one I am referring to was just a three minute job so no menu needed. I looked at Adobe help and it said that you could export to DVD and use the data for other authoring programs. Maybe this would be the answer, but I cant find a 'save to hard drive' option under export to DVD. Authoring programs tend to have this, so is it possible to do this from premier? Is avi the best way to render for DVD production? I do need the descent quality here. I have tried messing about with the interlacing stuff but not helping. Any ideas welcome. I am noit that technical so pleae dont tell me off for not giving enough info. Just ask specific if you need to know more. Please please, PLEASE ... if you must direct me to a website, just tell me what to do when I get there and which part to look at. Thanks so much