Yes, FCS 1 is compatible to Leopard, including Compressor!
Found the solution to your problem without going FCS 2: upgrade Qmaster 2 to 2.3 then upgrade Compressor 2.0/2.1 to 2.3, then 2.3.1.
I have FCP 5.1.4 on my Powerbook G4 15″ 1.5ghz, Mac OS 10.4.10 and finally got the newer Macbook Pro 2.6ghz (well, kinda new… its the last model before the awful unibodies). Was able to transfer everything over to the MBP, until I had the Compressor problem and the Motion problem (I found the solution to that too). Not gonna take credit, as I researched this the last 3 days online, from the Apple forums to people’s blogs to even Creative Cow. (Yes, I didn’t want to upgrade to FCS 2 either – hey, if its not broken, why fix it?)
Hope this helps.
Macbook Pro 15″ 2.6ghz, Powerbook G4 12″ 1.5ghz