Decoding high resolution video is a lot to ask of the little processor on your little tablet... I remember when my desktop struggled with it!

It is a bit of a pain, but the best thing to do is convert your videos to a more optimum format using this:

http://betalabs.nokia.com/betas/view...ideo-converter

Also, keep a lookout for video formatted for ipods/iphones because they work well on the tablet too.