I forgot to mention that the identifier of the package is "com.apple.pkg.ModbinKernel"

Here's a little how-to:

First you need to create a folder which will contains all files you want to add in you package.
As an example, the folder I created for ModbinKernel.pkg is named "ModbinKernel" (as you wish) and contains :
- mach_kernel
- mach_kernel.ctfsys
- System
--- Library
------ Extensions
--------- System.kext

You need to create the right folders like I did for System.kext

Once you have done, open /Developer/Applications/Utilities/PackageMaker.app.
Fill the "Organization" text field (i.e: com.apple.pkg or com.lawlessPPC.pkg)
Choose the Minimum target.
Click Ok.
Drag and drop the folder containing all your files in the content tab.
Give an identifier to your package (com.apple.pkg.YOURPACKAGE or com.lawlessPPC.YOURPACKAGE ... etc)
Click on "Contents" then click on Apply Recommendation (It should set the right permissions for all files in your package).
I say it should because sometimes ... it doesn't.

Click on "Build" or "Build and Run".

If you need to add some scripts I can explain you too. But not now !

:-)

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