hi. my name is rui i will answer your question regarding your problem about how to setup a compatible dvd decoder for sumsung external dvd drive.
1st of what's the model of yoursumsung external dvd drive?
2nd if you have a internet connection and know the model of your dvd drive you can download a compatible decoder for your sumsung(model)using google.
here is one that you can try out its a NVIDIA PureVideo Decoder (NVIDIA DVD Decoder) 1.02.186 (Samsung Dvd Decoder).
NVIDIA PureVideo Decoder is a combination of a hardware video processor and video decode software for playback of DVD and MPEG-2 videos using Microsoft Windows Media Player and Windows Media Center Edition.
you can download it @ http://samsung-dvd-decoder.fyxm.net/
it's easy to use just follow the instruction...
hope it helps you in anyway.^_^