Creating a stack in a dock

In the end part of the Leopard demonstration seen on the YouTube below, demonstrator selects multiple applications and drag it to the dock to create an application stack. I can't do the same thing in my Leopard. Is this function not available in released version?

http://jp.youtube.com/watch?v=p0RFqb_L9uQ

Make a normal folder and fill it with alias' for the apps you want. Then just drag the folder to the dock and bingo stacks.

Simple.

Yeah, I understand that the way you've written is the proper way. But in the video, there is no step of making a normal folder and just directly dragging the application icons in the dock. I was wondering if there is a tip to do that.