Broadcasting pink noise through your car stereo system is certainly one way to start getting a "look" at what how your system sounds. If you do that, you will want a microphone with a reasonably flat frequency response and an RTA that can display a spectrum in octave or third-octave bands, like SignalScope Pro. Pink noise should have a flat spectrum on an octave band analyzer.
An alternative to pink noise is white noise, which will have a flat spectrum on a narrowband (FFT) analyzer, like the one in either SignalScope or SignalScope Pro. FFT analysis lets you see the spectrum with higher resolution, particularly at higher frequencies.
In either case, I don't recommend using the built-in mic on your PowerBook. If you want an inexpensive measurement mic, you might want to consider the Nady CM100 or the Behringer ECM8000, both of which are electret condenser mics. You will also need an audio interface with at least one built-in mic preamp that offers phantom power for the microphone. I would recommend the Echo AudioFire 4 (www.echoaudio.com
) or the Edirol FA-66 (www.edirol.com
). Either will connect to your PowerBook via FireWire cable without requiring a separate power supply.
If you need to generate a white or pink noise signal, take a look at SignalSuite, as well. If you can't connect the audio output of your PowerBook directly to your car stereo, you can use SignalSuite to generate an audio file containing the test signal, which can then be burned to a CD.
I hope this helps you get started.