SOUND CARD :
The second important part (for software decoders) of your system is also the part which most people don't even think about when DVD decoding is concerned, the Sound Card. While many legacy ISA cards will work perfectly in Windows 95/98 and in your games, DVD decoding using software really do require a newer PCI sound card. You sound card should support 48kHz decoding (check as many only support up to 44kHz) as if it doesn't the software decoder will have to downmix the sound to 44kHz, which will require more CPU power. The PCI bus is also needed to transfer the sound stream information quickly around the system.
Hardware decoders don't really require a sound card as the sound is decoded on the card itself. But certain hardware decoders supports giving your SBLive audio card the chance to have 4 speaker discrete surround, like the Hollywood+ based range (DXR-3 and RealMagic Hollwood+). For software decoders, if your sound card supports 4/6/8 channel audio output (eg. Creative SB-Live range) then depending on the software player's hardware support level, your sound card can also support 4 (Dolby/DTS 4.1)/6 (Dolby/DTS 5.1)/8 (Dolby/DTS 7.1) speaker discrete output, certified Dolby Digital 5.1/Dolby Digital Surround EX/DTS audio output. While this feature also depends on the type of software decoder you use, both the latest versions of PowerDVD (4.0 XP) and WinDVD (3.0 DTS) will support 4/6 channel output (and 8 channels for PowerDVD 4.0 XP)