Why do I get errors when backing up files on my Mac?

I just bought a new 1tb external HD and want to backup everything from my old 320gb external HD to it. I realize that this will take time to transfer so much data, but I keep getting errors that are stopping the process completely. I have tried using just the finder option to basically drag and drop all the files from one HD to the other, most files will copy just fine but some files will give "Error Code 0." I have also tried using some freeware called iBackup, but it just ends up hanging after some time. Do I need to fix permissions or anything like that. I'm using Mac OS 10.5.4.