Well Im far from an expert, but I had a similar problem with Slackware 12.0 I could pull up the sound files and the software seemed to function correctly but I had no sound.
I ended up using alsaconf
from the term prompt. During the set up it will let you know that it sees your card and then it will set the volumes as it sees fit (you can change at anytime with alsamixer
Then still from the prompt (or command line for the true Linux users)you can use play
to verify the sound works. After that you can boot into KDE /Gnome and see what happens. Mine still didn't work immendiatly in KDE, but I rebooted. Ran a few more media players in KDE 3.5 when it came back up and after a few mins I activated XINE and the sound crackle and popped and BAM, I've had sound ever since.
I hope this helps although I realize it doesn't address the video. I haven't made it that far yet and am working on Networking