Photo gallery with thumbnails question

I’ve completed the tutorial to create a photo gallery using flash and xml, and have gone on to add the thumbnails. Everything works as intended, but now I would like to add another feature…

I’d like to highlight the thumbnail that coordinates with the current image (maybe at 100% alpha while the others are only at 50% or something along those lines). Any suggestions, building off of this: www.kirupa.com/developer/mx2004/thumbnails.htm ?