Ventrilo is a very popular software for voice communication and works very well or close to perfect on Ubuntu.
Ventrilo does not have a native Linux client. Therefor we need to install Wine before we can continue with the installation of Ventrilo.
Installing Wine is very simple, just launch the Ubuntu Software Center and search for Wine. Upon installing heavy configuration is not needed, but we do need to launch the Wine configuration at least once. The reason for this is that Wine needs to setup it's folder structure in your home folder.
Either browse your applications menu, search for Wine in your Unity dash, or open a terminal and type the following command:
As mentioned, there is no need to configure anything unless desired. Simply launch winecfg and close it and it will create the .wine folder structure in your home folder.
For detailed installation and configuration introductions see the Wine article.
To install Ventrilo you simply download the client at Ventrilo's website (this guide recommends Windows 32bit - XP, Vista, Windows 7) and run the installation file by double clicking it, just like on a Windows machine.
For more details on how to install Ventrilo and other Windows applications visit Installing Windows Applications With Wine.
Make sure your microphone is working elsewhere before troubleshooting.
If you desire Text-to-Speech you have to install SpeechSDK.
Other issues might be listed at WineHQ.
Mangler is an open source VOIP client capable of connecting to Ventrilo 3.x servers. It is capable of performing almost all standard user functionality found in a Windows Ventrilo client.
There are also several alternatives to Ventrilo that have native Linux clients. The most popular ones being TeamSpeak and Mumble.