Dowloading music to IPOD from 2nd computer

Hello,

I need to download music (a specific playlist) to my Ipod from another computer itunes library. I don't want to lose what I already have on my Ipod by the new syncing. How can I do this? I don't want to lose the new downloaded playlist when I sign back into my normal itunes library where it automatically syncs when it opens.
Any help really appreciated.