Mac OS X Leopard only: You already know how to view zip archive contents and even preview files in the Trash using Leopard’s handy Quick Look feature, and now you can look inside folders, too. Using a Folder Quick Look plug-in, instead of just looking at a big old folder icon when you Quick Look a directory, you can get a file listing of what’s inside. Here’s how to get it working.
-
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Download the Folder Quick Look plug-in. - Extract its contents into
/Users/YOU/Library/QuickLook/. Replace YOU with your
username. You may have to create the final QuickLook folder. Make
sure that the contents of the zip file go here (it’s four files
total; two are readme’s.) - Relaunch Finder by holding down the Option key and click and
holding on the Dock’s Finder icon. Choose “Relaunch” from the
context menu.
Then, just select any folder in Finder and hit the Space key to
Quick Look what’s inside. Here’s the result when I Quick Look my
Applications folder: 
Notice you can
also see hidden files and show the file timestamp using the
checkboxes at the bottom, too. Handy! The plug-in is a free
download for Mac OS X Leopard only. (Don’t forget you can also
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quick look multiple files at once as well, no plug-in
required.)