Audio in 64-bit Windows guests
By Fat Bloke on Jan 15, 2010
In case you haven't noticed, a lot of Fat Bloke's Blogs are reminders to self Here's another one...
If you have created a 64-bit Windows 7 virtual machine, you may think it is awfully quiet. This is because the 64-bit version of Windows 7 does not ship with drivers for the audio device (AC 97) which VirtualBox presents to the guest OS.
If you want audio you have to go get the drivers and install them yourself. I got mine from Realtek site.
Once you have installed them, and rebooted, you should get audio just fine.