Can't restore My iPhone 4 from iPhone 3GS backup?

Today my girlfriend got an iPhone 4 after her 3GS broke. She brought it home and went to register/set it up. We go to do the restore from back up and nothing happens. We wait for 15+ minutes for it to happen and all it does is make us do it all over again.

What is going on and why isn't it working?

I know there's a iPhone backup data restore software can extract the backup files onto computer, so you can try this way, extract your backup files and save it onto computer, then add it to iPhone 4 iTunes account. If you want to try, you can download the iPhone Backup Restore software from
http://www.iphonebackuprestore.com/