Screen Tearing in FCP 6

Hi
Have a FCP 6 running on my Macbook Pro, I keep getting screen Tearing in the Canvas window when i play any form of footage from DVC pro to DV, the quicker the cuts, the worse the screen tearing.. what causes this and how do i fix it? Have read MANY conflicting posts for this problem, some say its a screen resolution problem, some say it s a memory problem, some say its a data speed problem.. have yet to come accross any straight answer.

When i export the sequence out and play in Quicktime, its perfect, no tearing at all.
There is no options on the macbook settings to change it's screen resolution to test that theory, just says N/A in teh resolution field
Have tried running the canvas window at less than 100% as someone posted but alas, still tearing.. its driving me nuts , its so annoying, especially if you have someone watching the cut, really puts them off with the horizontal tearing.

I have 2GB of Memory and I am running the media off and ext firewire 800 drive.
Graphics card Nividia Gefore 8600

can anyone help me?

cheers
h