Normally I could just copy the "iTunes" folder from Music, and paste it into the Music folder on a new install, but when I did that in Lion, the library shows up blank.
When you start hold alt while clicking the iTunes icon to start the application, it will ask you where your library is. Point it to the Music folder. It will repopulate. This is also how you can put iTunes on another volume.
When you start hold alt while clicking the iTunes icon to start the application, it will ask you where your library is. Point it to the Music folder. It will repopulate. This is also how you can put iTunes on another volume.