Stream music on Android to Desktop speakers

Get a Male to Male 3.5 mm audio cable. Connect one end to your phone's audio jack and the other one to your PC's microphone jack.

Now here comes the tricky part :

1. In the notification area, right click the speaker icon. Click "Playback Devices".
2. In the Dialogue Box, right click "Speakers -> Set as Default Device". If there is already a green tick on the speaker icon, move to step 3.

3. If you have laptop then (A) or desktop then (B) :

   (A) Remove the cable you just connected. Now click on "Recording" Tab. See, there's a Mic which has a green tick. Don't interfere with this thing. Now the second one is a mic which is disconnected and has a red mark. Now connect the cable. It will show ready. Now double click it. In the popup, click "Listen" Tab. Check the "Listen to this Device". In the "Playback through this device dropdown, select Speakers. Now click apply. Your computer might now start producing awkward sounds, to adjust, click "Levels" Tab. Now adjust Microphone volume and Microphone boost to the desired amount to remove any sort of noise.
   
   (B) If you have a desktop, All the steps are same as a laptop except the microphone selection. In the recording devices menu, only one microphone should be there. So it is easy to find that. Do all the next steps as a laptop.
   

NOTE : If you can't see your device, right click and tick "Show disabled devices" and "Show disconnected devices". If your device is disabled, enable it first. 4. Now play any audio of your choice in the phone to get the desired output.

P.S. : Any device with a 3.5 mm audio output can be used as a source.

Yes you can. No additional soft or hardware required. Android 4.4.2 and WinXP. Like this: enable BT on both devices, make sure under Windows' BT Configuration->Local Services you have 'Headset' service set to 'Automatic startup'. Connect the devices (using pass-phrase if required), check on Android that 'Media audio' is enabled for the connected PC. Play some music, enjoy!

In case you haven't found a solution yet, I would recommend an app called Soundwire

Yes, you can do this in Windows XP and 7. It will stream all audio from the phone- apps, games, etc. You do not need any additional software, just Bluetooth connectivity on the pc. AirDroid lets you access your device, including streaming music, over WiFi via web browser.

You could also just plug your phone in USB to your PC, and play the music on the pc with MusicBee or any other media player.