Monitor won't play video help

I have a dual monitor setup…one side with newer dell monitor, the other with a samsung 931b monitor…we i try to play video, such as in itunes, the dell plays it fine but if i move it over to the samsung monitor it gets real choppy and slow motion video, its not even watchable, can someone help out as to why this is? thanks

How have you got the monitors set up? What video card are you using?

it is an ati radeon hd 2600 xt, i believe the dell is dvi and the samsung vga. i know the card has two monitor outputs and they are different