You can do it with the Windows Sound Recorder.
You should be able to find it at: Start Menu --> Programs --> Accessories --> Entertainment --> Sound Recorder.
If it isn't there, do a search for sndrec32.exe. That ought to work.
It's main limitation, however, is that it can record a maximum of 60 seconds worth of sound at a time. Same is the case with all the free sound recording software I've been able to find on the internet, sadly. I have spent hours, literally, just looking for a sound recording software which can record at least 6 minutes at a time! So far, I've been unsuccessful, does anybody know of such free software?