On the right hand side of ventrilo, there is a button that says setup. Click on it, then another page will appear. On the top left hand corner of that page you will see something called "push To Talk" Click the box next to it so it's on. Then go down into the "hotKey" box and click your mouse in it. Now push whatever button you want to be the button you use to talk with. For EX: my push to talk button is the 1 key. So when I talk I push down 1, I talk, then when Im done saying whatevert I wanted to I I let go. To make sure you set it up right, click the test button on the bottom and then push your PTT button and see if it works. Then push okay and you are done!
The reason I didn't respond was because I left the program running by mistake, sorry about that. But I'm glad a bunch of you were on!!!
-Mike
p.s. If you still don't understand send me a pm and i'll go into more detail.