Set up USB Headphones in Windows Vista

With your USB Headphones plugged into an available USB port.
Right click the speaker icon in the system tray - by default located on the bottom right of your display.
Choose Playback Devices. Right click the headset and then click the Set as Default button.

If you play games on your computer, the game or other program that uses sounds may reset your default sound device back to your speakers - so you may have to periodically go back in and re-set up the default sound device.

Headphones that plug into your sound card via the round connections are sometimes more user friendly, (depending on your situation) but if you are using the headphones for a phone, you will have to use your microphone input and your speaker output.

If your computer is on the floor and you don't want to crawl in the back, AND you have
USB connectors in the front of your computer, then in that case, the USB headphones may be more user friendly for you in the physical realm, but you will
have to deal with enabling and disabling them and re-enabling them through Windows, if you play a game or some other program changes the default device.
Like many computer issues, your experience may vary.