is the exported avi jerky?
if not, it's a problem at the encoding stage.
I'm not really au fait with tmpgenc's in-depth options, but what level of motion compensation are you using? are you definitely encoding pal>pal or ntsc>ntsc, not pal>ntsc or ntsc>pal?
What frame rate are you making it if you're doing ntsc, 29fps or 24fps? Does that match the original video?
AMD Athlon 1700 (@2200mhz from 1466 sod the noise!) - 768mb pc3200 - 200GB Maxtor - Pioneer 106 - GF4 Ti4200 - twinhan/visionplus pci dvb-t - random pci analogue tv tuner - A7v600-x (to replace the a7n8x-d that died...) - random 17\" CRT
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Konica/Minolta dimage z10 w/2x512mb SD;
A silly amount of Cat-5 and usb cables