Right, I think I solved the problem.
In your device manager, open up the configuration for the ethernet adapter and click the alternative called: JUMBO-something (norwegian OS, so not sure what to call it exactly). It's set to deactivated as standard.
I set that one to 9kb MTU and I set the PS3 to use 1500 MTU (although I'm not sure changing it on the PS3 was needed).
Now videos are running straight away and seem to go smoothly
Devvie83, thank you VERY much! I would try to change that option if i tried everything else)) Since I changed PC configuration and OS from XP to 7 I had this stuttering problem and couldn't understand what was the reason. Even now when all is working fine I'm curious about that mysterious Jumbo Frame.
I did just right what you said - changed Jumbo Frame (ENG OS) to 9kb MTU and that's ALL! Didn't touch ps3.
I have pretty new PC
motherboard MSI P67A GD65