Alex,
It would be more helpful in the future if you were more specific on if you solved the problem and exactly how. Links are always helpful.
That being said, continuing with Alex's suggestion, I went to Realtek's website and downloaded the driver:
http://www.realtek.com/downloads/
At the lower left, you'll see a link to "HD Audio Codec Driver." Download and install this. It solved my problem.
My setup and symptoms: Windows XP3 in a FAT32 formatted Boot Camp partition. After the update to XP3, the sound wasn't working. Sound worked fine in Leopard, but when booting into boot camp, no sound came from the speakers. Also, there was a red light coming from the headphone jack.