I'm using a Sound Blaster Audigy 4 with the latest Vista drivers.
About the only problem I've had was losing the front speakers when I was trying to reconfigure Media Center.
Reinstalling the drivers fixed the problem. (I don't use compatibility mode or 'run as admin', and they install just fine)
i got the conexant ac-link (ac'97) audio card to work, but the driver is not signed (windows dislikes this greatly), and i havent tried rebooting my computer yet. i will probably have to disable device signature enforcement every time i restart.
I have the C-Media AC97 onboard audio and it works perfectly. Using driver version 22.214.171.124. I also have Creative Audigy 4 Pro on this computer and even using the driver advised on this forum, it is crap! It works but produces distortion intermittently, the onboard sound doesn't have any issues.
One point of interest is that at work I installed Windows 7 on a computer that doesn't even have Vista drivers for it. It's an IBM M50 using Intel chipset. I downloaded the XP drivers for the graphics and audio, ran them in compatibility mode and both work perfectly!