Tranferring music from an itunes account on one computer to itunes on another

i just bought a new computer and want to transfer my music from my old computer to my new iTunes so I can sync my ipod. I get a message telling me my ipod can only be synced to one computer at a time. does this mean i can only use my old computer with my ipod? My purchased music has been downloaded but i have music loaded from tons of cds and movies. What can i do?