I don't use the software method. I just push one button next to my keyboard. It toggles between external speakers and headphones.
Computer Headphone Speaker Switch
I'm an owl, up all hours. The wife prefers to turn in early. To avoid the noise of my (powered) speakers annoying her they are fed through a timeswitch that turns them off at 10pm and on at 8am. That solves part one of the problem.
I have a USB heaset that I use "out of hours" when I need sound. That involves some clicking to change output device.
No big deal, but does anyone know a way to get Win XP SP2 to switch between "C-Media Wave Device" and "Logitech USB Headset" at a stipulated time of day?