You can lower each audio event's volume by clicking the top of the event and dragging downward. OR.. by inserting a volume envelope on the entire track. Highlight a track and menu select "Insert> Audio Envelope> Volume" or press the "V" key on your keyboard. Add as many envelopes as needed or until you see god.
Adding a compressor plug-in to the track may help also.
Is the Sony Compressor in Vegas 8 and Vegas 9 effective ?
You may need to adjust the Ratio and/or Threshold. A ratio of 1:1 will do nothing. 10:1 and above can be considered limiting. (subjective). Threshold adj. is dependent on the amplitude level. (Pull the Threshold fader downward to make it kick-in more on lower level sounds.) Try some of the pre-sets, then adj. to suit your needs.
Wavehammer is a two-stage compressor/limiter/volume maximizer which works well. (when used in moderation of course)
Make sure you do not have the plug-in/plug-in chains bypassed; individually or globally.