If you have an external storage device with enough free space, all you need to do is copy your iTunes folders from home/music/iTunes and home/library/iTunes and replace those folders on the new drive.
After that, when you open iTunes, everything will be as it was on your original hard drive.
If you haven't got an external HD with enough free space, you can connect your original HD through a caddy, and transfer the files like that! You can buy caddy's from various retailers, I'm not sure where you are based but you can get an idea here
Make sure you get a 2.5" SATA Caddy/Enclosure for a laptop HD or a 3.5" for a desktop!
(I'm assuming you're using a mac here, in regards to the file paths, not too sure what they would be on a windows machine, but shouldn't be too different!)