MBP no audio after 1.4 Bootcamp install, Sigmatel won't install, PCI device failure
Look in XP's device manager (Control Panel> System> Hardware> Device Manager> System Devices) for a PCI device with a yellow exclamation point. After my Bootcamp 1.4 install on a MBP there was one yellow marked PCI device. After I clicked on properties and manually repaired this device (telling xp to look for drivers on the mac drivers cd), I was able to re-run the mac drivers cd and the sigmatel and realtek drivers installed properly. (Unknown PCI turns into UAA Bus Driver for High Definition Audio)
Finally, working audio, horray! I don't know whether it is the fact that my MBP is an early model or that my XP SP2 CD is a funny version, but the audio drivers have been problematic every time I've had to reinstall bootcamp.