Yesterday, Microsoft's program manager for sound in Windows Vista (what a great title!), Steve Ball, posted aexplaining why audio playback sometimes gets glitchy in Windows.
There's an air of post-facto justification about the posting--it basically reminds us that a PC is doing a lot more things simultaneously than, say, a $20 CD player--but toward the end of the post, he notes that it's common for certain older device drivers to lock out the CPU for 10 milliseconds to 50ms, causing an obvious problem.
Of course, he didn't tell anyone just what those devices those drivers might belong to. He did promise a follow up post which will address the corrective action Microsoft will be taking.