Actually you can add tabs. They are really windows, not plugins (if I'm understanding you right). Here's a tutorial done by JR from VASST on youtube that will show you how:
It's about photomontage but starts by showing you how to access US for the first time. There are lots of free tutorials by VASST on Youtube. Just search on VASST training.
Enjoy.
Randy
Do you have Vegas Pro 8.0 or 9.0? Ultimate S Pro will only show up as a tab in v8 or v9. If you use Vegas 6 or 7 it is still a script and can only be placed on the toolbar as John said. In Vegas Pro 8 or 9 go to View | Extensions | VASST UltimateS Pro 4 | UltimateS Pro 4. If you look under the Command Tabs menu ( View | Extensions | VASST UltimateS Pro 4 | Command Tabs) you will see the individual 15 tabs that can be docked separately. This allows you to make your own tab configurations.