"Should I try using different software decoding?" I would try Cinemaster, WinDVD or Power DVD and see what happens
StonedWheat.
"How do I utilize the DVD hardware decoding in the Viper 2?" Like a lot of cards this videocard
assists the processor in decoding. And it should do so automatically or by checking off preferences of the dvd setup program your using.
If your Creative Labs DVD decoder card is the Dxr3 Decoder card then its really a Sigma Designs Hollywood plus card.
http://www.creativelabs.com/pc-dvd/dxr3-decoder/
http://www.sigmadesigns.com/products/hollywood_plus.htm