Q: Where to find iSight startup app & how to use it

I have a 2009 MacBook Pro with a newly re-installed 10.6.8 OS.  I want to use iMovie HD with iSight and it doesn't "see" iSight.  iMovie & iSight worked fine with the old OS install but I tried out one of the newer OSs so I could use Dragon Speaking - and didn't like the new OS.