According to this USA Today piece, Guitar Hero 5 owners will be allowed to import up to 35 Guitar Hero: World Tour tracks to their new game. For a charge.
“Immediately, players can import 35 songs from Guitar Hero World Tour for 280 points on Xbox Live and $3.50 on the PlayStation Network,” said the article.
“Later this fall, songs from Guitar Hero Smash Hits can be imported, too.”
Guitar Hero 5 ships on September 11. Just checking this with Acti now.