I have Final Cut Pro, 4.5 and am running it on OS 10.3.9 with no problems previously. System info:
Machine Model: Power Mac G4
CPU Type: PowerPC G4 (3.3)
Number Of CPUs: 2
CPU Speed: 1.25 GHz
L2 Cache (per CPU): 256 KB
L3 Cache (per CPU): 1 MB
Memory: 1.75 GB
Anyway...