The standard Ventrilo server license allows you to run an 8-slot Ventrilo server on your machine. You can download the server software from the Ventrilo website at: http://www.ventrilo.com/download.php
To run more than an 8-slot server, you would need to become a Ventrilo partner. Flagship (the company behind Ventrilo) is extremely selective in choosing new partners and requires a minimum purchase of 1000 slots, so this can be a daunting task. If you aren't planning to start a large Ventrilo business, it would probably be best to order large servers directly from us at https://www.nfoservers.com/order.php?type=ventrilo
. We also have a reseller program that you might consider taking advantage of, if you'd like to offer these servers to your customers.