Currently Being ModeratedFeb 4, 2013 8:54 AM (in response to zarrath)
Yes. That's how it works. You can only manually manage/sync media with one iTunes library at a time. You must erase the media on the phone when switching libraries.
Copy the media from your old computer to the new one and import it into iTunes. Then you can put it back on the phone after setting it up to use media from the new iTunes library.
Currently Being ModeratedFeb 5, 2013 3:17 AM (in response to zarrath)
Also, follow the steps given here...