I downloaded the new audacity program, my operating system is Mac OS 10.7.4. I’m using a little walkman cassette player,a griffin iMic and the relevant connection. When I play a tape the sound doesn’t come through the computer speakers (the sound is on ); all I hear is high pitched squealing noises.
I’ve looked at the set up tutorials and the audio midi picture does not match what’s on my laptop.
Help! 
If you’re on Lion, then, no, the pictures may not line up.
As a first step, Audacity > Preferences > Recording. Make sure Overdub…, Hardware…, and Software… are all turned off. Then, on the device toolbar near the top of Audacity, make sure you’re recording from the iMic and not the internal microphone.
http://manual.audacityteam.org/help/manual/man/device_toolbar.html
Click once inside the red recording meters and they will wake up and meter the sound coming in. Play a CD. You won’t hear anything yet, but the red meters should bounce.
http://kozco.com/tech/audacity/Audacity1_record.jpg
Let us know if you get this far.
Koz
In Devices there is no other choice apart from Built in Output and built in Microphone. Do I have to plug in the iMic before it is detected? Sorry I’m a total newby at this! 
You have to plug the USB end of the iMic into a USB port on the Mac before launching Audacity. If you plugged in iMIc while Audacity was running, click Transport > Rescan Audio Devices at the top of the computer window.
If Transport > Software Playthrough or Transport > Hardware Playthrough do not let you hear the audio while you are recording it, you can obtain LineIn ( http://www.rogueamoeba.com/freebies/ ) .
Gale