Video is choppy when reproducing in fullscreen, how to fix it?

view full story

http://askubuntu.com – Videos is choppy when I play in fullscreen. Its the same with downloaded movies and youtube. I have no idea why. I have tried using kplayer, kmplayer and vlc with downloaded, but it is all the same. How do I fix the chopping...easily? My computer is like 1 years old... but I'm not really used to linux/kubuntu so I don't know how to solve it. So I hope some kind soul out there can help me. (HowTos)