Guitar Hero: World Tour, Guitar Hero: World Tour DLC, and Guitar Hero: Smash Hits songs will work on Guitar Hero 5.

For PS3 and Xbox 360 owners, a free update will be available to enable Guitar Hero: World Tour DLC backward compatibility. To use the songs from the old games, however, a “nominal re-licensing fee” will be charged, and you’ll need to have saved your manuals so you can use the 20-digit code from them.

For the Wii, DLC must be redownloaded. There will also be an individual song copy option for importing disc-based games from Guitar Hero: World Tour.

Source: Joystiq