Description of problem:
Sound Device AC97 cannot be recognized in Windows 2008 R2 SP1

Version-Release number of selected component (if applicable):
kvm:kvm-83-232.el5

How reproducible:
always

Steps to Reproduce:
1.boot guest with the following cmd -
  /usr/libexec/qemu-kvm -rtc-td-hack -usbdevice tablet -no-hpet -drive file=/opt/win2008RSP1,if=virtio,boot=on,werror=stop,cache=none,format=qcow2,media=disk -smp 2 -m 2G -net nic,macaddr=00:12:24:58:a1:2f,model=virtio,vlan=0 -net tap,script=/etc/qemu-ifup,vlan=0 -uuid `uuidgen` -boot dc -balloon virtio -notify all -monitor stdio -vnc :3 -soundhw ac97 -cdrom /opt/en_windows_server_2008_r2_standard_enterprise_datacenter_and_web_with_sp1_x64_dvd_617601.iso -name win2008r2-64 -fda /usr/share/virtio-win/virtio-drivers-1.0.1-52454.vfd 
2.log in OS and open device manager
  check sound device
Expected results,The sound device works correctly.At least,the drive is loaded successfully.
Actual   results,Warning says that the drivers of this device are not installed.
And try to install driver manually but fail.

Additional info:
kernel version:2.6.18-260.el5
Not reproduce the issue on windows xp