Using the Canon 5D mark2 for video means you can produce movies at 1080p resolution. Normal DVD does not support this level of quality so unless you have a Blu-Ray player you will be unable to view your Canon 5D2 movies in their optimum resolution.
However there is a solution that doesn't involve the expense of getting a dedicated bluray player. You can use a Western Digital Media player (WD Player) connected to an external hard drive to play your movies on an HD TV at 1080p resolution. This does require an HDMI cable to get the best possible picture quality.
I have tested a cable purchased for £4.99 from Sainsburys and was amazed by the quality from such a cheap component when similar cables are available for up to £100 and more. Which magazine have today published a survey that shows exactly the same results for HDMI cables and recommend the cheaper cables as being the best option.
The quality from the Canon 5D2 video played at 1080p on a Sony HD TV is stunning and really shows the benefits of the large format sensor on the camera. Once Canon release the same control features as available on the Canon 7D then the camera will be an awesome piece of kit.