You could try ‘free musiczilla’…….. I’ve used it before….. but I can’t remember why I don’t use it now….
Depending on the version of Windows [assuming you’re using Windows of course…] and Audacity you’re using it should be fairly straight-forward. Though I will admit, I’m having a bit of issue with Audacity’s 1.3 beta [on Win7].
I remember using Audacity 1.2 on my previous computer [WinXP] and there was a selector drop-down next to the level controllers with your source selector. For some odd reason, they got rid of it for the 1.3 release. Now you have to go through the preferences [in the edit menu] and then go to the "devices" tab. In the "recording Devices" box, there’s another 2 drop-downs, one with a list of available devices [Microphone, Line-In, Stereo Mix*, Etc.] and another the choose the "Number of channels" to record.
*If you’re using Win7, "Stereo Mix" doesn’t show up right away. To use it [which you’ll need to record from MySpace, and the like…], right click your volume icon, and click "Recording Devices". From there, right click inside the box of choices, and select "Show Disabled Devices" and "Show Disconnected Devices". Once "Stereo Mix" shows up, Right-Click it, and select "Disable", which should remove the check mark, enabling you to use "Stereo Mix"