For the library:
Edit->Edit Preferences->Library->Move Library
For the music files:
Select all files
Right Click->Send To->Folder (Move)->Move Files to Organized Folder
To Folder = Your new base music folder
Template = Whatever you want.
If you're not sure whether all of your files have the relevant tags, uncheck "Do not reorganize files with missing naming tags"
If you have artwork, etc in folders, make sure "also move remaining non-media files" is checked.
==OR==
If all of your music is 100% under a music folder (it's not scattered around in different places) AND you want to keep it as it's currently organized...
Move the entire music folder from the old drive to the new drive as-is, then use File->Library->Relink Music File Paths to remap the old location to the new location (eg C:\Music to D:\Music)
Should be a pretty clean process.