Jerky play from CD
 

I have a problem with a few movies: They play jerky from CD, but when copy to HD, they play fine. (This problem happens to only a few Divx movies, most are played well)

I guess that the CD buffer is too small, so I go to System-> Performance-> CD buffer, there it shows: "No read ahead" I changed to "Quad speed or higher" to get a larger buffer, reboot and check the CD buffer: it reverts back to "No read ahead" again! :x

Some one could please tell me how to fix that? (what line in Registry refers to CD buffer?) so I can edit it directly.

My system:
PIII 667Mhz, Win98SE, 512Mb Memory
Nvidia G4 MX440
Clone CD and Paragon's Virtual CD (Could these 2 virtual CD drive reset the CD buffer?)