Tested OK with Win7PE_SE Release using Virtual PC 2007 and on real PC with Realtek High Definition Audio.
Realtek High Definition driver script.
Edit:
Updated link to audio.script v7
v7
Added the Service Multimedia Class Scheduler (MMCSS)
v6
Registry fix x64 and added WMware x64 audio driver
v5
Added the possibility to add your own drivers, thx ChrisR
v4
Included fix by JFX, now audio activates itself (no more audio Activator)
v3
Improved support for browsers
v2
No more need to install driver 2 times.
Some drivers included. (VIRTUALAUDIO, AC97)