Your ventrilo logs can be found in the "File Manager" tab of your NFo control panel. Just use the drop down list to select "Log" and that will pull up all info from people connecting to what the admins are doing.
To ban a range of ip's from your ventrilo just right click your ventrilo name inside the ventrilo client, login as admin then under admin select ban. This will pull up the ban manager where you can enter the range of ip's you wish to ban.
<Spray> Please try locking your modem in a closet, or facing it towards the wall in the corner, so it knows its misbehaved