DVD-ROM without software

OK, I bought a Quality DVD-ROM about 2 months ago. It works great so far with reagular CDs, but wont play DVDs cause I don’t have the software. I’ve seen these DVD Decoders at the place I bought the DVD ROM, but its about as expensive as the ROM itself. Do I need this DVD Decoder, or do I just need some software? If it is software, where do I get it?