There are special programs for this, for example KRec in KDE or gnome-sound-recorder in (guess what) .
You will have to set your mic to capture mode. This can be done in pretty much any mixer, like KMix, alsamixer, amixer or w/e. While you're in the mixer, you can turn up your mic's volume to test the hardware and connexion. If the recording app doesn't pick up the input, turn up the capture control in the mixer.

Audacity can also record.

I use rec from the sox commandline utilities. Unless you want to do something special,

rec file.wav
<talk, play your guitar, whatever>
ctrl-c

does the trick.

Thanks for your help guys, now once I find the microphone I'll be able to test the programs I've just emerged.

dylunio

just use headphones as a mic - they do the trick for me...

When I read "use headphones as a mic" I thought "WTF is this guy going on about??" - but they do work well as microphones, I've used the mic boost in alsa mixer, and gnome-sound-recorder, and I'm recording my strange voice to the disk.

Thanks a lot for all the help guys;

dylunio