Ben Armstrong writes over at his popular Blog site, Virtual PC Guy, about some of the changes to the new virtual machine wizard in Virtual PC 2007.

Now, he describes how when you select the operating system for the virtual machine during the wizard creation process, there is a new difference.  Previously, it just defaulted to memory and disk size.

Ben writes: 

Normally Virtual PC creates virtual machines with an ISA Sound Blaster 16 sound card.  This is compatible with most operating systems, except for Windows Vista (which no longer supports ISA cards, 'cause lets face it, that stuff is quite old and getting rare these days).  But, if you select "Windows Vista" as the operating system that you are going to install when you are creating the virtual machine, the virtual machine will be created with a new Vista compatible sound card (for the curious, this is a synthetic sound card that only has drivers for Windows Vista).

Now, if you create a Vista virtual machine but choose another operating system in the new virtual machine wizard, you will have no sound.  In order to fix this, just use the new virtual machine wizard to create a new virtual machine that uses your existing virtual hard disk, and make sure to select "Windows Vista".

Read the original and leave Ben a comment, here.