Leopard will not let you just select a group of files and make a Stack from them. You can only make a Stack from a directory (folder). So, to get Word, Excel, and Powerpoint into one Stack I did the following.
- I created a directory under /Applications/Microsoft Office 2004 I called OfficeApps.
- I selected the three applications, did a Make Alias for each (right mouse button when selected), and moved the aliases into the new folder.
- I then dragged the folder to the right side of the Dock.
Now, when I click on the Stack, I can click and select the application.