You want to do HD on such old hardware? Well good luck...
As for the sound card, I have a Sound Blaster Live 5.1 here. I suggest you find an official one as the OEM ones are harder to have support for. I have a SB0220 and once configured properly, it does 5.1. It also provides Optical (SPDIF) in and out, but I believe there's no official connector for it. I just used a Gygabyte motherboard optical riser card and along with some specs, modified the connector according to the sound blaster spdif connector and voilĂ . I haven't tested it yet, but the LEDs do light up so I guess that's a good start