07-19-2011, 10:04 AM
+1 to what zarathu has said. Once you've trashed them, you'll have to "re-educate" iTunes so that it looks for the tracks on your back-up drive.
You should also change the default location of where iTunes normally stores its music/media files. Do this by opening the iTunes preferences, go to "Advanced" and you'll see a panel that says "iTunes Media folder location".
By default, iTunes is set to keep all of your music files in a sub-folder of your user account on the System Drive. This is usually:
Users / my username
/ Music / iTunes / iTunes Music
This is all very well on a new machine with only one HDD, but considering the many gigabytes of media files that people tend to have these days, in the long term it isn't a very clever place to keep them.
IMHO, a good habit to get into is to keep your System Drive strictly for the OS itself, OS-related stuff and other applications, and store all of your personal stuff - music, video, pictures, documents etc. - on other drives. If you can make it so that your System Drive has oodles of free space hanging around doing nothing, your Mac will thank you.
And if you're buying an extra HDD, don't skimp on the GB - buy the biggest you can afford!