You know already how easy it is to record audio into your computer with a microphone (for a reminder, see our article How to Use the PC Recording Studio You Didn’t Know You Already Had). But did you know you could also record whatever audio is already playing in Windows - on your sound card - also? It isn't as obvious how to do this, but below is a good article that will show you step-by-step. It comes in handy if you want to record things like Skype conversations (just make sure you tell the other person first!), webinars, music from internet radio or YouTube, etc.
It focuses on Windows 7, but the concepts are the same for any version of Windows.