For those that are new to ventrilo here is one setting that will be a lifesaver.
If you have a player that is coming through too loudly or too softly you can adjust the volume for that person. That volume level will be remembered for as long as that person logs into Ventrilo with that username and ip address. To set the volume level do the following.
Right click on the person's name and select "Miscellaneous"
Next Select "Special Effects"
You will have a selection of choices displayed. You will want to select Volume and add it to the left hand column.
Next you will click on Properties and you see a slider with which you can adjust the volume up or down as needed, from 0% or off to 800% which is an 8 fold increase.
I hope this helps :-)