Not of the flashing button but what button you are asking about. In Vista the start button vanished with just ONE and only one button on the bottom left of the toolbar which many call what was the start button.
Here's a picture of what we see today -> http://www.cnet.com.au/story_media/339282210/vista-start-menu.jpg
See the Vista flag on the bottom left? Now tell us what button you see flashing.
This is on my Acer Aspire 5100 notebook running Vista HP with SP1. Recently this started; the little round START button flashes on whatever window happens to be onscreen. A VERY fast flash. I've done all I could but it still flashes. Any suggestions?