Right click on the speaker icon and choose recording devices.

Now you will see the sound window right click and choose show disabled devices

Find Stereo mix this may be called mp3 or what u hear and right click and select enable.

Now you done this lets right click and un-check show disabled devices to hide the disabled devices and we no longer need them.

Now we got that stuff out the road you wont have to do this again now on to the fun part! Right click on Stereo mix (as stated before could also be called what you hear or mp3) and select set as default device.

And now you can play music however you might want to set the level for this so your music not blasting for others or to low to do this right click on stereo mix (as stated before could also be called what you hear or mp3) and select properties.

Choose the levels tab and adjust the slider best bet would be to set it as 1 play the music ask them how it sound if it to low crank it up till u get it right!

And that it when finished and you want to talk just set the microphone back to default by right clicking it and choose set as default

done