Re: burn dvd in iDVD for 7 second clip-16:9 aspect is ok but burn same 8 min sequence 16:9 is not right

Not remembering much about how FCP 4.5 flips out, I would guess Quicktime Conversion is the culprit if everything remains the same otherwise. It seems like the wild card.

I think exporting your timeline as a Quicktime Movie (not QT Conversion) and sending it to Compressor is a step you need to take. At least it would verify if it's FCP or iDVD giving you the problem. I never learned Compressor either, it's pretty intuitive when you start clicking around.