I might be getting a new Ipod video, but I already have an Ipod Nano. Is there a way to switch the Ipod that your itunes recognizes if you get a new one? Or will my music I've bought only work on the old Ipod?

No no, that music is now yours. Simply plug in the new iPod and all data should be transferred to it.

You'll be able to put all of the music already in iTunes on your new iPod, as well as keep it on your old iPod if you want to. The only limit with music purchased from iTunes is that you can't put a song on more than 5 computers.