If I am using Premier Pro CS3, and upgrade to CS4 will my programs like Magic Bullet and Cineform work in the CS4 version or is there a bunch of re installing to do?

Your mileage may vary... depends on what add-ons/plug-ins you have to install...

In my case I installed CS4 and then started to add all of my add-ons/plug-ins...

everything seemed to work and then pow... one of the plug-ins totaly wiped out
the media encoder...

I'd suggest you contact the OEM of the plug-in to make sure its compatable... could
save you some time and agrivation in the long term...