Yeah I'm also having this problem in WPF/E on WinXP Pro SP2. I'm using Nvidia audio (info below)
Still blown away my the graphic capability though!
www.vista.si

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Sound Devices
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Description: NVIDIA(R) nForce(TM) Audio
Default Sound Playback: Yes
Default Voice Playback: Yes
Hardware ID: NFORCE_VAD
Manufacturer ID: 1
Product ID: 100
Type: WDM
Driver Name: nvapu.sys
Driver Version: 6.14.0465.0000 (English)
Driver Attributes: Final Retail
WHQL Logo'd: Yes
Date and Size: 7/26/2005 06:01:56, 415360 bytes
Other Files:
Driver Provider: NVIDIA Corporation
HW Accel Level: Full
Cap Flags: 0xF5F
Min/Max Sample Rate: 200, 100000
Static/Strm HW Mix Bufs: 20, 17
Static/Strm HW 3D Bufs: 16, 16
HW Memory: 0
Voice Management: No
EAX(tm) 2.0 Listen/Src: Yes, Yes
I3DL2(tm) Listen/Src: Yes, Yes
Sensaura(tm) ZoomFX(tm): No
Registry: OK
Sound Test Result: Not run