I was looking forward to the “Stacks” feature of Leopard; I miss the option of dragging windows to the edge of the screen to turn them into tabs, and I thought Stacks (ill-fatedly née “Piles”) might provide some of the interface sensibility the OS X Finder lacks. Alas, it seems as though Stacks only work when the Dock is at the bottom of the screen, and since I position my Dock on the right (I usually need vertical screen space more than horizontal), I’m out of luck.
run the update to 10.5.2, and i believe you will be back in luck
Rest assured it work on the right or left, even without upgrading to 10.5.2. But if you DO upgrade to .2 you get the folder function that I missed when upgrading to Leopard. I have commented on this at Targuman and feel free to email me if you have any questions. I will see what I can do to help!