Download OriginalExpose and run Install Script.app. That's it.
Ok, summing up, I did my own version of the very good result (the DockHack) out of a macrumors topic, by psid, and I want to share with you guys directly here, as this is a very proper and simple solution.
The only problem is we still need to download the files, which are extracted from a Dock.app remainescent from Snow Leopard beta, that still used the Original Expose from Leopard (and before).
Since there's a file to download anyway, I've added a Install Script to it, which will apply something similar to the following commands below (except it won't move itself anywhere). You can optionally replace "SL-bak" to anything you want to backup your "Snow Leopard" dock to:
mv ~/Download/OriginalExpose ~/
sudo cp -R /System/Library/CoreServices/Dock.app /System/Library/CoreServices/Dock.app.SL-bak
sudo cp ~/OriginalExpose/Contents/MacOS/* /System/Library/CoreServices/Dock.app/Contents/MacOS/
sudo cp ~/OriginalExpose/Contents/Resources/* /System/Library/CoreServices/Dock.app/Contents/Resources/
update: Looks like Lion will have a better expose and I hope this whole post becomes useless after it. But, meanwhile, this still works perfectly fine even with 10.6.8! :)
I can't imagine how this would look on the bad one: