Stacks is one of the selling points of Leopard, and many users love it. Many, but not all. If you'd like to use hierarchical menus in Leopard, try one of these three solutions.
Quay 1.0 was released last week as shareware (here is our post about Quay). For €7, Quay provides custom-sorted hierarchical menus, re-sizable icons and a customizable dock icon. Undocumented APIs are not used, and Quay isn't a hack. If you only want to use one Quay Dock icon it is free, but you'll have to pay for the program to use two or more.
Also available is freeware HierarchicalDock by Eternal Storms Software. To create a hierarchical menu, simply drag a folder onto the application's icon. You can opt to preview your files with Quick Look instead of icons, and sort items by last used date or creation date.
Finally, check out OldFolder. It's free and open source, so you can fiddle around with it. Simply launch it and browse to the folder you'd like to use (support for multiple folders is possible, too).
There you go. Three ways to go "old school" on your dock. Enjoy.