The Old Ringtone Way
Find the file of the song you'd like as a ringtone. (Click on the song, then "Get Info," and finally "Summary" to get the file location.) Duplicate the file and put it in another, separate directory. Change the file extension of the duplicate file to .M4R.

If you are a Windows user and the file extension doesn't show up, go to the Explorer menu above your file and choose "Tools," then "Folder Options," and finally "View". Click on "Hide extensions for known file types" to turn that option off. The extensions should show up and, once changed to M4R, the file type should say "Ringtone."

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Now open up iTunes and literally drag and drop the new file into your library. It may take a few tries, but it will show up under the "Ringtones" tab. It will also be available to upload to the iPhone when connected. Files under 3MB tend to work best - anything larger usually isn't accepted. And for whatever reason, some songs just don't work. It is a trial and error method.

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Post-iTunes 7.4.1.2, the net is packed with suggested backdoors - more file extension changes and the like - but few, if any actually work. Right now the most sensible option is independent software, and the most popular software is iToner from Ambrosia. A trial version is available right now - and, unfortunately, is only for the Mac.

iToner creates a pseudo-iPhone interface on your desktop. Grab the desired music file, drag it into the iPhone mockup and, after loading up the desired ringtones, "Sync" the iPhone to transfer the music. The best part that it reads both MP3s and AACs.

The official copy of iToner is available for $15 from Ambrosia's Web site. That's the cost of about 15 Apple-sanctioned ringtones… if 15 are available in your library.

About the Author
Damon Brown wrote the "Pocket Idiot's Guide to the iPhone" (Alpha/Penguin Books). Available on August 7, you can preorder it at Amazon or your favorite online bookstore. Damon also writes for Playboy, SPIN and The New York Post.