In Device Manager the sound card should be listed by name (eg SoundBlaster Live or Soundblaster Audigy or whatever make it is). If it's not listed by name it means the driver for it is not installed, in which case you should see "Unknown Device" listed there with a red or yellow symbol.
Although XP has many drivers built in for the most popular soundcards, some it doesn't have so you have to download them from the makers website. I don't know enough about your soundcard make/model to assist you further.
As for not being able to play DVD-films. Windows XP (ie Windows Media Player) cannot play them without first installing software which contains the mpeg2 decoder. The easiest way of doing this is to install a dedicated DVD-player application. You will then be able to watch DVDs with that or use WMP -- whichever you prefer. You can download one from here:
http://www.microsoft.com/windows/win...r/plugins.aspx