What is the easiest way to transfer iTunes to an external hard drive?
Depending on your iTunes settings your music and stuff within iTunes might be scattered around your Hard Drive. If you want to move all of your iTunes Library you will have to enable the Media folder organization:
1. open the iTunes settings
2. go to Advanced
3. enable "keep iTunes media folder organized"
Close the settings and click on File > Library > Organize and select to "Consolidate files".
Now you can close iTunes and move your entire iTunes folder to another place and or Hard Drive. If you moved it iTunes will ask you to select a Library the next time you start it, as an alternative you can keep SHIFT pressed while opening iTunes and then select the moved iTunes Library.
If you are talking about the music files, you simply copy and paste the iTunes folder located in your "Music" folder (Vista & 7) from your account. In XP it would located under "My DocumentsMy Music".
The iTunes program cannot be copied over, just the media contained within.