MBP crashing on video and slow, slow FCP/Motion

Hi,

I recently (Jan2010) purchased a new MBP 15, with 4GB RAM and 7200pm 500GB Hard disk.

The main reason for buying it was to do video editing on FCP and Motion.

However FCP on this machine seems really clunky, i.e. everything has to be rendered before you can even see an effect. Is this normal? I don't have this on my old work PC with CS4 Premiere Pro. And it sometimes crashes, even on titling.

Also, Motion is really clunky. It doesn't show me any fluidity when playing back even basic sequences... just jumping.

And when I even just play videos on QT or rented DVDs the computer just crashes about every half an hour. Proper crashing too, with no mouse movement or anything.

Can someone shed some light on this?

All the forums I read before buying this MBP, said FCP and Motion would be fine!!!

Cheers,

Andrew. (in LONDON)