a friend and I shot a short film these days. And like most we got to do the editing now. The problem is that when i import the video in Premiere cs3 if not rendered it freezes constantly, it doesn't play smooth, and if i render it flashes in different colors, but runs smooth(as if there is some color filter over the video that changes). Are there any plug-ins that i should use, please help

the pc is a laptop running win7 and the hardware is a intel core 2 duo (t7100) at 1.8, 2gb ram, hd2600 video card.
I'm editing the material from an external hard drive at 7200rpm. (but it's the same effect on the HDD of the laptop./laptop's hhd is slower on rpm i'm not planing on editing from there.)