Syncing an iPod touch with a New Computer

A friend of mine has finally decided to start using her mac more fully (address book, mail, etc.) and she needs to sync her iPod touch with it. The problem is that she put music onto it from another computer when she first got it and she has been downloading applications on it and not syncing those to any computer. I have the music bit sorted out, but I am not for sure about the applications. I don't want to lose all of the application data, but I need to get it synced with the new computer. How do I go about doing this?