This is a fix if you are see the following message during installation;
"The installation failed"
"The installer can't install some files in Library/Application Support/GarageBand/Instrument Library/Plug-in settings/Drum Kits"
"Contact the software manufacturer for assistance"
Please follow the following steps to fix this problem:
(IMPORTANT note before proceeding: If you already have other instruments installed of your own, or perhaps from other packs such as Apple Jam Packs, you will most likely want to avoid them being replaced. To merge the World Pack instruments with your existing instruments, you should FIRST follow the instructions further down this mail under the heading "Merging World Pack Instruments with Your Existing Instruments")
How to install to a different location
You can use Disk Utility to make a blank disk image.
1. Open Disk Utility, located in 'Applications/Utilities', don't select anything in the Disk Utility window.
2. Choose File > New > Blank Image from the menu
3. Type a name for the disk image and choose where you want to save it, i.e. 'WorldPack' on the Desktop.
4. Set the size of the disk image from the Size pop-up menu to Custom 2gb.
5. Leave encryption method set to none.
6. Leave format set to read/write disk image, then click 'Create'.
Now run the installer (Install Zero-G WorldPack Instruments.mpkg) from the DVD and select 'WorldPack' as the destination.
Run the installer and select the external HD
Now follow EITHER (A) or (B) below:
(A) Merging the World Pack Instruments with Your Existing Instruments:
If you already have other instruments installed of your own, or from other packs such as Apple Jam Packs, you will most likely want to avoid them being replaced. To merge the World Pack instruments with your existing instruments, follow the above instructions for installing to a different location, but then, in order to copy the files over to your system without replacing any existing instruments, you need to manually go and get all of the ".pst" and ".exs" and ".cst" files that are within their relevant folders within the new disk image or external drive. They can be found within folders at the following location:
[New location you created] / Library / Application Support / GarageBand / Instrument Library
....and copy them all (so that you are adding them) into the corresponding folders within the following location:
Your HD / Users / Your User Name / Library / Application Support / GarageBand
Then restart your Mac and Trash the WorldPack.dmg on your Desktop or the Library folder on your external HD.
Run GarageBand and it should now see the new WorldPack Instruments as well as your own previous library of instruments.
(B) How to quickly copy all the World Pack instrument files over to your System if you don't mind REPLACING any existing instruments in your system:
In the finder select WorldPack or your external disc and drag the following directory in red to the directory in blue.
>Library / Application Support / GarageBand / Instrument Library
To your HD / Users / Your User Name / Library / Application Support / GarageBand
Select Replace in the copy dialogue.
Now restart your Mac and Trash the WorldPack.dmg on your Desktop or the Library folder on your external HD.
GarageBand should now see the WorldPack Instruments.