My 160 gig hard drive, in my laptop is full- I would like to move my music, itunes to an external drive and have itunes fine it there when I log on- how do I do this?

When you need to restore your backed up iTunes Library from your external hard drive to your computer, follow these steps:

Quit iTunes.
Locate your external hard drive.
Mac: On the Desktop or Finder sidebar.
Windows: In My Computer

Drag the iTunes folder (backed up earlier) from your external hard drive to whatever location you desire on your internal hard drive. It is recommended that you choose the default location for the iTunes folder, which is:

Mac OS X: /Users/username/Music
Windows XP: \Documents and Settings\username\My Documents\My Music\
Windows Vista or Windows 7: \Users\username\My Music\
Open iTunes while holding down the Option key (Mac) or Shift key (Windows).

In the resulting dialog, click the Choose Library button.

Select the iTunes folder you just moved to the internal hard drive.
Click Choose.