I saw this little gem on another forum. It's a plugin to automatically reconfigure the video output levels so that video displays on a PC in the same way that it will on a TV/DVD.
Video levels is something that take a lot of discussion under Vegas so I'm not going to go into it here. However in summary when editing on a PC and creating video for a TV (DVD, BluRay etc) use the following steps:
Install the plugin as per the instructions on the web page.
If using video scopes uncheck Studio RGB.
Set the plugin to "PC".
Edit with colours that actually look like the the final output with no need to uncheck boxes on render.
Get it here:
http://vegasvideo.de/extension-previewlevels-en.html