Photoshop Workshop

Digitizing Sound

You can easily add sound files using iTunes, and the iTunes Library appears in iMovie, iPhoto and iDVD so you can select what you want while in those programs.
The most convenient, and cheapest, way is to simply import the content of CDs you already own into iTunes. See iTunes Help for information on how to do this.
You can buy many songs in the iTunes music store. Hey, they're only 99 cents!
Some Internet sites have music you can download for free. This is often illegal, and the RIAA has been known to sue people who do this, and they almost always win. Such files are also often of very bad quality. It isn't worth it.

I use Sound Studio to record, connected to my iBook from my stereo using iMic from Griffin. See this article. Unfortunately the prices have gone up: Sound Studio is now $80 and the Griffin iMic is $40. It does come with a free recording program, Final Vinyl.
There may be free solutions, depending on what you have. You can try the open source program Audacity to record, and, depending on the model of your Mac, you may have sound input jacks already built-in. If you have iLife, you can record in GarageBand. If you already have Roxio Toast you can use CD Spin Doctor
Regardless of the method and the cost in dollars, keep in mind the cost in time and effort. If you choose to record a thirty minute vinyl record or tape, the recording process will take 30 minutes. If the recording has no pop, hisses, rumbles and so on, it will still need to be processed to assure the volume levels are correct, which takes about 5 seconds per minute for Normalize, and the same for DC Offset. If you need to edit out other problems it will take significantly longer. Unless you are very strapped for cash, or the music you want is simply not available on CD or from the iTunes Store, it probably isn't worth it.

In addition to things mentioned in this article:

Go to System Preferences, bring up the Sound pane, click the Input tab, and select your source.
Check the preferences in your recording software to make sure the input source is correct.
You may need to adjust the volume, either in the program or coming from the source; for instance, using the head phone jack on my stereo I have to adjust the stereo's volume control to get the correct input level. If the input level is being pinned at the end of the red section, your input is too loud, you'll get distortion. If the level of the loudest passages never gets into the red at all, it is too low, you'll need to adjust the volume upward.
The recording will be in AIF format, which slurps up 10MBs per minute, so 30 minutes of sound will take 300MBs of disk space. So make sure you have plenty of free space on your drive!
There are some programs that promise to clean up the sound automagically. They are pricey and don't always do what you expect. If your vinyl is old expect to spend a significant amount of time fixing the problems.