Itunes More then One Computer

iTunes subscriptions are tracked using a file called ITunes Music Library.xml. which is stored on your computer. This file keeps the log for both music files and podcast subscriptions, and is set up for the first time when you register your Ipod in Itunes on the specific computer.
The file is not web-based, so each iTunes library is linked to each computer.

It is possible to download songs from an iPod to more then one computer, but this wont share same download library.