Mac OS X 10.7, 10.8: How to use Migration Assistant to transfer files from another Mac - http://support.apple.com/kb/HT4889 - "You can use Migration Assistant in OS X Lion and Mountain Lion to transfer important information, such as user accounts, applications, network and computer settings, and files, from one Mac computer to another via a FireWire cable, ThunderBolt cable, or via an Ethernet or wireless "
If only concerned about iTunes:
iTunes: How to move [or copy] your music [library] to a new computer [or another drive] - http://support.apple.com/kb/HT4527
Quick answer if you use iTunes' default preferences settings: Copy the entire iTunes folder (and in doing so all its subfolders and files) intact to the other drive. Open iTunes and immediately hold down the Option (alt) key (shift on Windows), then guide it to the new location of the library.