If you have a PII processor or better you don't need a hardware decoder. All you need is a software decoder/player, you shouldn't play your DVD's with Media Player.
I had the same prob. when I got a dvd drive for free without any software.
I searched the internet & found a great player for free from
www.7thzone.com but the link doesn't seem to work any longer.
Some vid cards ship with a DVD player so check the cd that came with your vid card there might be one on it.
If not I could try to e-mail you the exe for the player that have just let me know.
Chef