Ripple is an internet protocol. It's ledger is kept on servers all over. In fact, I am in the process of installing RippleD and connecting my server to the broader network.
Watch these short youtube videos:
Here's an overview of Ripple ...
Here is an explanation of Ripple in 60 seconds ...
Here are two more videos:
Here is a video to help you understand how a Gateway works ... http://www.youtube.com/watch?v=M16ZatXbmLg
Here is a video to help you understand how the consensus ledger works ... http://www.youtube.com/watch?v=pj1QVb1vlC0
Then you should do a search on the Ripple Wiki and give it a read. (I'd send a link, but again, they're limiting me to two :-S )
Cheers!