How can I open an exclusive audio output in Windows XP?

I want to use the system's mic in/speaker out jacks to measure and fix voltage drops, but I cannot do this reliably without ensuring that my program has exclusive control of the audio. Is this possible in Windows XP? I have read about various API's that are available (WaveOut, Mixer) but have not found any information on taking exclusive control of an audio device before Windows Vista or 7.

Apparently the WDM kernel streaming API could possibly take exclusive control of the sound card, but this is undefined behavior. I can always work around by disabling the sound card by default in system settings, but this is less than an ideal solution (because it would still be possible for other applications to use the sound card).