My Macbook Pro plats files fine in h.264 and I can edit with ProRes all without skipping.

Which graphics card do you have?
What is your hard drive speed?

If you have the Early 2008 17" (no black glass), then your processor should be at least 2.5GHz and your graphics card should be NVIDIA GeForce 8600M GT with 512MB.

It is more than likely you opted for the larger capacity hard drive at 5400rpm and not the 200GB at 7200rpm. Check this by getting the model number of your internal drive from Disc Utility and copy/paste that into Google to search for specs. If you do have a slow drive, you can pick up another drive at 7200rpm and install it yourself.

These were your HD options:
250GB 5400-rpm Serial ATA hard drive (hard to do HD)
200GB 7200-rpm drive3 (fastest for video)
300GB 4200-rpm (slowest)

my god!
 

This is my hd: seagate ST9160823AS serial ata 2, 160GB, 7200rpm, graphic card the same as yours, but with 256mb. I think I cannot change it without changing the whole motherboard, right?

So... your files are playing without skipping now? Problem solved?

My advice is try playing the files from an external firewire drive.

David, I wrote this (I'm just getting used to write fro this forum)

This is my hd: seagate ST9160823AS serial ata 2, 160GB, 7200rpm, graphic card the same as yours, but with 256mb. I think I cannot change it without changing the whole motherboard, right?

I tried to play it from an external USB 7200rpm hard drive but didn't work.

thanks

If you are still having playback issues on your computer, try using VLC player. Quicktime will not play back the clips smoothly on my computer but VLC player will.

It looks like it comes down to your graphics card. You can upgrade the card yourself.

For reference, my Macbook pro has the 512MB graphics card and can play everything fine. My Quad-core Mac tower (G5) has a 256 and not everything is as smooth.