Is there a way to stream audio into the microphone port without jacking the speaker audio cable into the mic port? Operating systems: Windows, Linux
Assuming you want a virtual solution -- for example, you want a) to use some software to play an MP3 on a computer, and b) to use some other software to record that audio output on the same computer, you want something like JACK:
See the JACK FAQ for how to use it, and the JACK download page to get the source tarball; a Windows installer is included. For Linux, your distribution's software repositories (apt-get, yum, etc) already include JACK binaries, so you can use your preferred package management tool to install it.
On Ubuntu, you want to install the packages "jackd", "jack-tools", and possibly "qjackctl":
Windows 7 has the ability to play an mp3 player through the mic port to speaker. I think they call it microphone listening or something. You could probably record from the mic port then.
EDIT: see this link Lifehacker.com.au