Personally I would keep the "My Music" folder where it is, but just transfer all of the contents of the folder over to the new drive.
Although there are methods for moving the My Documents, My Music, and My Pictures folders elsewhere, I wouldn't do so because there may be times when you need to save a file into one of the My Documents sub-folders, or in My Documents itself, and then realise that the external drive is turned off, or is disconnected. You then have to cancel your action, turn on or connect up the external drive, then start again.
Also, using an external drive, it will not connect immediately when you start Windows, and so the Operating System will start looking for My Documents on Startup and fail to find it.
There are methods for moving the My Documents goup of folders, and Microsoft's guidance is here;
But this is what I would do;
1] When the external drive is up and running, create folders on it using Windows Explorer or My Computer for your own use, eg;
Marks stuff, and inside that, sub-folders called
My Documents, etc.
Of course, you can choose what names you like.
2] Copy and Paste All of your music files, photos, videos, etc from the current My Documents folders to the new ones. I say Copy and paste instead of Cut and paste because if anything goes wrong with the Cut command, you may lose all of your files. With Copy, you have another chance. Once the new files are tested, then you can delete the old files if you wish.
Use Windows Explorer or My Documents to navigate between the different folders to do the copying and pasting
3] Then test a couple of files by double clicking on them to make sure they still work.
4] Once you are happy the copy pasting has gone ok, then open up iTunes and start creating new playlists.
There is a way to keep the iTunes orginal playlist but point it to the new location. Instructions below;
5] Re-organise any photo's lists as needed using the software you usually use for viewing photos.
6] After a while, delete all the old files in the old My Documents folders.
I hope that helps.
A friend has a desktop computer running XP Home Edition and just a 30GB hard drive. His drive is full primarily from music (iTunes) and photos. If we added an external hard drive, how can we move My Music folder to that secondary drive?