Hi Steph, this support article describes how you can do this on a Windows PC. Please note it does depend on your PC hardware and the version of Windows you are using.
Hi Kyle, being able to transmit the audio from your computer into the conference call on a GoToMeeting depends on your computer. Some have the StereoMix option and some need to use audio patch cables to feed the Stereo Out back into the computer. Both methods are explained in this support article: Plaing Audio From A Desktop