[iMore.com]

If your Mac's hard drive is getting full, you can move your entire iTunes library to an external hard drive to free up space.

Full story from the iMore Blog...

[mikefward]

I've got the same problem as StephenO2. Everything was going like clockwork — I held down the alt key on my Mac whilst opening iTunes, Chose Library and the Get Info key shows me the track is still in its original place after I selected the External Hard Drive as the destination of the new Library. Fingers crossed you can bring closure....

[lemony0]

I've been thinking about doing this for a while to keep the storage almost full notice at bay. Why Apple sell us laptops with so little space I've no idea.