Hi -
A quick way to do this in FCP 7 is to select a lens flare from the Generator Button, the button that is on the lower right of the viewer (with the "A" on it).
Choose Render > Lens flare
!http://www.spotsbeforeyoureyes.com/LensFlare.jpg!
This will load a lens flare into the viewer. Edit it to the track above the video you want to place the sparkle on for about the duration you want it to be on. Then Control - Click on that clip in the timeline and from the drop down menu, and select Composite Mode > Add.
Double click on the clip of the lens flare in the timeline and, using the motion tab and controls tabs for the clip that are in the viewer, you can adjust the look of the effect so that it resizes, twirls and fades.
Hope this helps.
