Tipster site OneTipADay.com tells you how to use iTunes to embed album art in MP3 files so it'll appear in other applications.

Start iTunes on your Mac or Windows computer. To make a ringtone, it's not necessary to connect to your iTunes Store account, since you'll be working with an MP3 file located on your own hard drive.

An independent PC developer has created a program that lets users of Apple Computer's iTunes software share MP3 files almost as easily as they could using programs such as Kazaa.

Users will have to drag the MP3 file of your choice to the iTunes library. Click the tab named “File” at the top of the iTunes screen. Click the option named “Add to library”.

I have a ton of MP3 files, most have proper tags but some don't. I want to add album art to all of them and embed it in the MP3 file itself. I don't want to do it manually.

"A problem that I've been running into starting with iTunes 6 and continues into 7 is malformed ID3 tags when iTunes converts from WAV or Lossless to MP3.

iTunes for Windows sports the same features Mac users have grown accustomed to in their software — the ability to burn their audio files to CDs and rip files from CD to MP3.