[derekge]

Guess what: I had the same problem and I got it fixed. It seems that Vista loads a MS driver for my ASUS onboard sound: SoundMax AD1986A Audio WHQL. There is no driver from ASUS for Vista. The speakers work great but the headphones wouldn't output anything.

It's the default audio device setting: control panel | sound | playback tab | right-click headphones and select set as default device. I had to reboot iTunes after but it worked. Of course I had to change the setting back to get the speakers to work again - it's either or, not both.