well gwen announced that the dvd was coming out on her website.
and a no doubt forumer messaged her choreographer sho-tyme on myspace and he said that the serious video was recorded specifically as an extra for the dvd. there's a video on youtube called 'sho-tyme reel' or something that has a clip of serious.
and he also said that they were getting ready to shoot the video for "wind it up" this month, and it should be out in november sometime.
beacon-street.net is a pretty reliable fan site for info and is updated quite frequently.
edit: here's the video
http://www.youtube.com/watch?v=Ep0q9gfK9qQ&eurl the serious clip shows after the shakira and black eyed peas clips.