os 10.5 install / archive trouble

My system: G4 Quicksilver 1.2GB processor, 1GB Ram. I was running FCP 4.5 HD on OS 10.3.8. I upgraded to 10.5, but then my FCP would only capture 6 minutes at a time, then freeze up. I heard others were having problems with FCP after upgrading to 10.5. I wanted to just go back to what I had before, so I re-installed 10.3 from my previous install discs using "Archive & Install", but now all of the programs I had before appear on my desktop, and when I go to the "Previous System 2" folder, my FCP won't start.

Is there any way I can go back to the 10.5 setup I had before my 10.3 re-install? I'll then just upgrade my FCP from 10.5 and hopefully live happily ever after.

Thanks a lot!