Alright, i used to run Ubuntu for about 18 months and have set it up on over a dozen computers
You need to give more information, i don't particularly care what hardware you've got, but you said you've got 8.04. Is it a Fresh install? What packages have you added and removed.
in a terminal type $ $ dpkg --get-selections > /specify path maybe "'/home/username/Desktop/installedfiles.txt
If your new to the command line spaces are VERY important in UNIX and UNIX like systems. If for some reason you need a space in the name of your output file use a escape character like this. this\ is\ how\ you\ put\ spaces\ in\ UNIX
What video and audio files are you trying to run
Ubuntu by default has a very comprehensive package list on a fresh install. Coupled with its repository list of over 1500 packages its a very good choice for beginners and even experienced alike. standard install i do believe the default player is totem and the standard audio player interface is rythymbox.
None of these will play propriety codes unless you have those codecs installed. Ubuntu is so well written for beginners that it should prompt you when trying to play a .mp3 say and ask you if you want to install the relevant codec. First up open up a synaptic (add remove software) and find totem, and select it and mark i for removal. Then once taht is completed, find totem-xine. accept all of its requirements. then search for gstreamer.
install good bad and ugly this will give you basically all codecs to open almost any file
after this if your computer tries to open a codec it doesn't have ti will prompt you to install the relevant package.
Fedora Core 10 AMD platform
University student B.IT.
Change text size in ubuntu 9.04