Here's a link to download the Ventrilo client.
If you have Windows i386, 32bit, Win2000, XP, 2003, Vista, 2008 : http://www.ventrilo.com/dlprod.php?id=1
If you have any other operating system, click here to find yours on the list and follow the link to the download. http://www.ventrilo.com/download.php