I've got a 17" PBook 1.67, 1.5 gigs Ram, Finale 2006, OSX 10.4.2
This is still under the minimum specs
I just loaded up 5 saxes, 4 trumpets, 4 bones, bass, drums & Piano. Whenever the full ensemble played together, I was getting mild stuttering. This was using all "lite" instruments. I could have done a little more tweaking to reduce the cpu load, but I just wanted to give to an "out of the box" example of what to expect.
To use JABB & Finale you'll need a faster computer, or compose in Finale , then import a midi file into a sequencer. By freezing tracks and converting midi tracks to audio in a sequencer, you'll be able to get by on a slower computer.