Sound too quiet with headphones

While running WinXP on my MacBook with Boot Camp, the sound is at a normal level with the speakers, but when I use headphones, it's FAR too quiet! The maximum volume is about the same as the middle volume on the Mac end of my MacBook with heaphones.

Any way I can make the headphone volume louder? I've played around with the volume controls already, but I can't get it to go any higher...