Try right clicking in the video window, and you can change preview quality.
The better you make the preview quality the more chance of it playing jerky etc. It will need to be rendered first to play back in full quality.
2 x 21\" HITACHI super contrast monitors.....2 x 200 gig HDD\'s....2 x 512mb dane-elec pc3200.....TV in card (cheap and sh!t!)....3.2 P4 HT....BOARD - ASUS P4C800 - C delux (fsb 800mhz DUAL DDR 400)....GRAPHICS - ATI 256ddr POWERCOLOUR Radeon 9600XT (500mhz/400mhz)....MATROX RT.X100 real time editing card