Desperatly in need of help

omg i'm so frustrated with my ipod!!! I just got it back from sending it in and wanted to put music on it right away. But it's not registered or anything, so it won't show up on itunes and I can't put my c.d's and stuff on it. But the problem is I lost the disk that lets you register your ipod. How do I register it now?!? Do I have to like pay a ton of money to get a new disk or should I just buy a new ipod that doesn't suck as much as the mini? Please help!!