...I have just got a new MacBook Pro and have put my mums iPod into it and opened iTunes. I want to add some songs from my iTunes library into her iPod, but its not letting me, saying its synced to another computer.
The problem is if I sync it with my computer & iTunes library, its going to delete all the songs which are already on it.
Anybody know how to prevent this from happening?
Well, yes. That has been the basic workflow limitation since 2001. Normally, she has those songs on her computer, so if you were to sync the iPod to your computer it would wipe out all content from the iPod; you could then sync again to her computer to put the iPod back into the same state it is right now, so if she has those songs on her computer, there are no worries there.
But an iPod is not the conventional way to move music TO a computer. Once she syncs her iPod to HER computer, it will wipe out anythng you might have just put there, and you are right back at square one. An iPod sync only moves music FROM a computer TO an iPod, and not the other way around, and it regularly deletes all content from an iPod not represented already locally in iTunes on that computer. There are 3rd-party solutions out there with varying levels of success and cost, but you don't really need to get that far under the hood to do what you want to do.
The easiest solution is to find the songs inside your iTunes folder on YOUR computer, copy them through the Finder to a flash drive, install the flash drive on HER computer, and use the "add to library" command in iTunes to move the content from the flash drive to her computer. Then she can sync HER iPod to get those songs portable.
There is one caveat, which is if any of those files were purchased from the iTunes store during the period when DRM was in effect (2003 to about 2010), her computer must be authorized to your iTunes account, which is done in iTunes on her computer.
