PKGView is a tool for extracting files from PS3 PKG. Tool is 100% legal it contains no code Sony.
PKGView also has a graphical interface that simplifies the extraction of both individual files and the complete package.
PS3 PKGView Version 1.3 Changelog:
Added support to psx/psp packages.
Added Windows 7 Taskbar progress.
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To quote, roughly translated: PKGView is a file extraction tool to debug PS3 PKG files. This tool 100% legal it contains no code Sony.
PKGView has a graphical interface that simplifies the extraction of both individual files and the complete package.
Note: This version is very limited and only allows you to extract individual files, it can not remove folders or create PKG files.
Finally, UnPKG requires the http://www.microsoft.com/downloads/en/confirmation.aspx?FamilyID=a7b7a05e-6de6-4d3a-a423-37bf0912db84&displaylang=en to run the exe file linked above. Props to emot for the news!