Post the make/model of the computer. Processor speed plays a big part. There are open source drivers and proprietary drives depending the graphics chip manufacturer, so check the hardware, I think it's under System Places or something like that. I'm on a Windows box right night and haven't used Ubuntu for a while. What format is the video, avi, mpg, mkv, etc? What software are you using for playback, Mplayer, VLC, etc? For linux newbies I usually suggest Linux Mint as it comes with the necessary multimedia codecs. Don't be afraid to visit the Ubuntu Forums for a lot of useful information. There aren't many Linux users here at Myce but we'll help if we can.