If you're on Win7, I don't think there is a reason, unless you need the features of something like ffdshow, to use anything but the MS DTV-DVD decoder. I've never had any of the problems that some people report with freezing, etc.
HTPC: E7500, Nvidia 9500GT, ATI Theater 650Pro PCI/Firewire Network Recorder/Avermedia Duet A188, NPVR 2.6.2, Win7 Pro
Test: Asrock 890GM Pro 3, Athlon X2 255 , internal HD4290, ATI Theater 650Pro PCIe, NPVR 2.6.2, Win7 Home Premium
Lounge: Athlon 3200, Nvidia 7600GT, Network Recorder, NPVR 2.5.5, Win7 Home Premium