I want to add some simple acoustic guitar tracks to an iMovie video.  Can I use a small diaphragm condenser mic (like the Rode NT3) with a 9 volt battery, run it through iMic, and record directly into iMovie, just as if I were adding a voiceover?  Or do I definitely need a preamp?  How about doing that same thing with a pickup (like the AKG C411)?  Any alternative suggestions would certainly be appreciated.

An acoustic guitar needs a decent microphone to sound anything close to good. A live vocal-type dynamic mic won't do the trick, and even that would require a preamp of some sort. Better would be a condenser mic, some which have a battery for power, but you'd still need the preamp. If no battery, then the condenser also needs phantom power from whatever you're plugging it into.

In sound quality a pickup would lie in-between. Still need a preamp.