Adding a closed thread to Vbulletin

Hello, I have a forum and I want to give a free gift for new users. What I like to do, is have a forum, or a thread that everyone can see and I write some promos on that thread. However, if the end user wants to get the free gift, I like to force him to register to the forum. After he is registered he/she can download the free gift. Is that possible to accomplish? If yes, please be kind and explain in details. This is a Vbulletin version 4