i recently got a 5.1 surround sound system, and i have 3 audio ports on my computer, one for speakers one for microphone and another one... my friend told me theres a way to change the output on the microphone so you can plug the rear audio plug into the microphone jack and recieve sound.
Change the output on the microphone? The microphone is an input NOT an output. Has your friend actually done something like this? This one I'd like to see...but bottom line...you can't do this. Your friend is an idiot and should not be giving out stupid crap.
What you need to use is an audio output from your PC. They are usually the jacks that you use to connect powered speakers. These are low level outputs that can be connected to a receiver. What you need are mini stereo plugs to RCA adapter. You can get this from Radio Shack and it connects from your PC to your receiver's analog stereo (Left/Right) input.
Be aware though that connecting your PC to a receiver is not ideal and you may get a lot of interference.
By the way, don't forget to tell your friend that he is full of crap
Don't take his advice unless he has the benefit of experience. That's like taking sex advice from a virgin.
your friend isnt crazy there are SOME motherboards or sound cards that can change the mic & line out ports into 5.1 outputs but it all depends if your equipment has these feature