I found a couple of sites you could try:
Vista News - Nieuwste Vista Drivers 3
down the page gives this link:
RipTide Audio Device
ftp://ftp.hp.com/pub/softpaq/sp23001-23500/sp23455.exe
or this:
http://www.bioticaindia.com/download...e-audio-device
or this:
Rockwell Master Riptide PCI Audio Device Driver Windows Info
This says it's for W2000/XP, but who knows?
Is your Riptide a PCI card? Without having that card, it's impossible for me to test. Hopefully you may get lucky.
I know that when I used my Realtek AC97 onboard sound, the volume was low, even with powered amp/speakers. After switching to a Azuentech X-plosion Cinema 7.1, the volume increase was amazing. If all else fails, you may unfortunately have to buy a new card.