I worked with the 10.6.3 install DVD and opening "/Optional Installs/Xcode.mpkg" with Pacifist revealed a bit different layout than described in the linked blog post. For me Property List Editor was here: Contents of Xcode.mpkg / Contents of DevToolsHIDDEN / Contents of Developer Tools.pkg / Applications / Utilities / Property List Editor.app
The required framework is at the location as can be expected based on the above example: Contents of Xcode.mpkg / Contents of DevToolsHIDDEN / Contents of Developer Tools.pkg / Library / PrivateFrameworks / PlistEdit.framework
You should right-click both in Pacifist and select "Install to Default Location". Once they're installed, you've to move them to /Developer/Applications/Utilities and /Developer/Library/PrivateFrameworks respectively. PLE won't work from the default locations, the moving of the app+framework is a requirement!
P.S.: all this is necessary even on Snow Leopard since the 4.2 Xcode installer seems to have removed Property List Editor.