iTunes: How to move your music to a new computer - http://support.apple.com/kb/HT4527
do not confuse moving your whole folder and library with moving just media files as in
iTunes for Mac: Moving your iTunes Media folder - http://support.apple.com/kb/HT1449
Quick answer if you let iTunes manage your music: Copy the whole iTunes folder and all its subfolders and files intact to the other drive. Start iTunes with the option key held down and guide it to the new location of the library.
Macworld - How to transfer iTunes libraries between PC and Mac - http://www.macworld.com/article/46248/2005/08/shiftitunes.html