Using more then one iTunes library

It is sometimes very useful to have more then one iTunes library. You can free up space on your hard drive by having just the essential and having the rest on an external. This can be particularly practical with a portable where you carry a part and have the rest at home on an external or your network. At first glance, iTunes doesn't seem to support this but it can be done by holding the Option key when loading iTunes 7. It will then ask which library to load. Screenshot here: