I wish to move my iTunes library from my PC to an external drive to make room on my PC. How do I do this?

The following may help: http://support.apple.com/kb/HT1364

Note the following fine print therein:

Note: If you move your library to an external drive, you'll need to power up and connect the drive before starting iTunes. If you don't, iTunes will prompt you to either locate the library or to create a new library (which will result in an empty library). No matter what, it's always a good idea to have a backup of the media you have in iTunes.