[jitter] capturing & editing clips for jitter with Fcp

Dear all i want to understand once for all wich settings are best for me to capture, edit and save clips in Fcp for jitter. actually my clips doesn't play smooth as max example media clips.
when playing my clips in jitter sometimes i get undesired glitches and hiccups (while example clips not) and if i reproduce them with other programs (Qt player, modul8) they are ok...what am i missing???
how the example clips have been prepared, edited, saved?

my needs
play low res (320 240) clips for realtime visuals as smooth as i can

my system
alu Pb 1.ghz osx 10.4
jitter 1.5...
Fcp 5.0

my camera
canon xm1

fcp settings
capture preset: dv pal 48hz

sequence settings
frame size:720 576 ccir 601/dv pal 5:4
pixel aspect ratio: pal ccir 601 720 576
fielddominance: none  

saving settings
export>quicktime conversion>options:
compression photo-jpeg medium
no sound
size 320 240
no optimization for streaming

any helps and thoughts are GREATLY appreciated
ciao
michele