Video playback problems

I am fairly new to blender and really new to the VSE and anyway I was trying to import some video i wanted with green-screen into blender so i went to the motion tracking tab and opened it up put when i hit alt-a to play the video it plays really slow. Is this normal or do i need to change something, i already set the size and fps to the correct amount but it still is slow. Is my computer not strong enough to handle it cause the video is full HD and the computer is dual core 1.8 Ghz with 2 gb of ram. I’m guessing thats not really enough.
Also i didnt know where to post this cause there is no place for video editing stuff.

Figured it out it was the computer.

blender doesnt like movie clips! open the clip in the vse as normal but render the whole thing out to a PNG sequence and use the PNG’s to work with.