virtualbox.org

After a lot of googling, downloading, unzipping, installing and starting all over, I finally found the sound drivers that would permit me to have sound on Windows 7 beta (at least up to build 7077). Note that I'm running VBox 64bit Win7 guest on a Linux host (kernel 2.6.29).

Here's the link:

http://www.microsoft.com/communities/ne ... &sloc=&p=1

If you would have searched here, on the forums, then you would have found out that running Windows Update will give you the AC'97 driver for Win 7.