I feel your pain.
I started a new project in CS3, imported a 34 minute clip, selected a 2 minute section, inserted to timeline with 1.5 seconds of “Black Video” at each end and exported for DVD. The Export progress bar indicated 65,000 frames! I stopped it and checked the timeline and it showed just the 2 minute clip, in fact the visible timeline extended only to 12 minutes! It did then export the entire 34 minutes with no black at either end and no poster frames either.
Opened the same project in CS4 with no changes and exported as expected.
It seems CS3 has issues with black video??