Sent to you by Vihang Shah via Google Reader:
Add Album Art to any Music Folder
This is easily my favorite tip! One of the coolest new features in Windows XP is its album thumbnail generator, which automatically places the appropriate album cover art on the folder to which you are copying music (generally in WMA format). But what about those people that have already copied their CDs to the hard drive using MP3 format? You can download album cover art from sites such as cdnow.com or amguide.com, and then use the new Windows XP folder customize feature to display the proper image for each folder. But this takes time--you have to manually edit the folder properties for every single folder--and you will lose customizations if you have to reinstall the OS. There's an excellent fix, however.
When you download the album cover art from the Web, just save the images as folder.jpg each time and place them in the appropriate folder. Then, Windows XP will automatically use that image as the thumbnail for that folder and, best of all, will use that image in Windows Media Player for Windows XP (MPXP) if you choose to display album cover art instead of a visualization. And the folder customization is automatic, so it survives an OS reinstallation as well.
Your music folders never looked so good!