Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
I don't know how much more I can elucidate. Basically, my Mac has recently decided to switch to my Finder menu every 30 seconds, doesn't matter what program you're in. So, the top menu bar changes to the Finder menu bar, everything else remains as is. I just have to click my working window to jump back to the program I was working with, but boy, it can get annoying.
 
Are you using 10.4.11? And have Stuffit AVR installed?

If so then try this:

Open System Preferences
Click on Stuffit AVR on the bottom row
Press stop


If you don't have Stuffit AVR installed then it would be worthwhile opening up Utilites - Console and seeing what is going on when it jumps back to Finder
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.