Vista Movie Maker and Stuttering Preview

Just got a new laptop Dell 1520 Intel Dual Core 1.66Ghz 667Mhz with 2GB of
ram and a dedicated Nvidia GeForce 8400M GS graphics card 128mb.

The problem is when in Movie Maker the preview plays fine for 40 seconds and
then starts to stutter both on the preview and the sound. I have not yet
tried to make a dvd to see if that is smooth, but even if it was, it makes
editing a real pain.

I have tried making the preview pane as small as possible with still the
same result.

The file I am using plays fine in Windows Media Player.

As I bought the laptop for editing, I am wondering if I can get this problem
sorted out.