I recently had some issues syncing my ipod touch with my imac. In preparation for the eventual wiping of the imac (I was getting the dreaded “Unknown error when attempting to sync ipod” error which pretty much means your itunes is screwed) I transferred the contents of my library to my new macbook pro.
The copy was fine but what I really wanted was the software for the January update that had all the gmail, maps and other fun applications. I could see that I had ordered it through itunes but when I reset the ipod touch it no longer kept that software. The apple help was particularly unhelpful in this regard and kept on telling me to sync with the original computer.
I finally found this website - http://forums.ilounge.com/archive/index.php/t-220475.html and therein my answer lay. Perform the following steps prior to wiping your original computer:
The iPod touch January Software Upgrade can only be synced to iPod touch from the primary iTunes library. If the user is manually managing music and video on iPod, this is the computer where they first set up the iPod or first set it up after restoring the iPod. The “iPod touch App Pack 4A93.ipa” file can be copied from the computer where you purchased it to your primary iTunes library computer, and sync the iPod from there.
The file is located here:
Mac OS X:
~/Library/iTunes/Mobile Applications
Windows XP
C:\Documents and Settingsuser name\Application Data\Apple Computer\iTunes\Mobile Applications\
Windows Vista:
C:\Usersuser name\AppData\Roaming
Apple Computer\iTunes\Mobile Applications\
Note: These locations are hidden by default in Windows. You can these locations by choosing “Show hidden files and folder” in the View tab of the Folder Options Control Panel.
Once you have copied the “iPod touch App Pack 4A93.ipa” file to the computer with your home library, make a new folder named Mobile Applications in the correct location, and place the “iPod touch App Pack 4A93.ipa” file there. Open iTunes and sync your iPod touch.