I would assume that the Vista boot problem is probably the bigger problem. Googling for "dual boot linux vista" will give you a lot of results. You haven't provided details, so I can't sort it out for you.
The sound problem: you basically need to use the sound configuration tool provided by your Linux distribution. I never used MEPIS, so I can't help with that. You can just as well try to a Linux system from a LiveCD (Knoppix or Fedora or similar) and see if sound devices are recognized by default. Knoppix is very good on hardware detection. You can also try to install Skype, which uses it's own ways of audio access - at least you will know if audio access works at all.
Last edited by Tinkster; 10-30-2010 at 03:27 PM.