I would suggest installing the application called compiz-switch.
I don't know if it is approved here, but it works fine for me on Felicia and Elyssa. Compiz is great but can be a nuisance when anything involving video or flash is used.
Here is the link: http://forlong.blogage.de/entries/pages/Compiz-Switch
This software allows the user to completey enable or disable compiz with a single click of the mouse.
Try then to see if your video is choppy when playing DVDs
Also check if you have hardware acceleration by typing Glxgears in a terminal. If you are above 500-700 frames/sec(???), then you are ok. Under this you may need to look for drivers as suggested by AK Dave.