How do you render a video to fit the screen? In other words, how do you get rid of the black bars around the video?
The black bars are created when your source footage doesn’t match the aspect ratio of your final file. For instance, if you deliver a project as 16:9 widescreen, but you use 4:3 source footage in that project, you see bars on both sides of the video. Similarly, if you use widescreen source footage in a 4:3 file, you’ll see bars above and below your footage. In any case, you can use the Event Pan/Crop tool to remove the bars. In the Event Pan/Crop window, right-click the position box and choose Match Output Aspect from the menu. This crops your source footage so that its aspect ratio matches that of your project (which you’ve presumably already set to match your final output). Keep in mind that doing this actually crops some of the image out and you’ll have to decide whether that’s more or less desirable than living with the black bars.

If I have mixed media on my Vegas Pro Timeline, what should I set my Project settings to?
That’s a bit of a tricky question. Since Vegas Pro has less calculating to do when your project video properties match the properties of the footage on your timeline, you might want to set your project properties to match the type of footage you’re using most often in your project. You should see improved frame rates on preview playback.
However, it’s important to know exactly what your project will look like when rendered, so you have to be careful. For instance, say the file type you use most often in your project has a 4:3 aspect ratio, but you’ll be delivering in a 16:9 ratio. If you follow the advice above to achieve maximum frame rate on preview playback and set your project to 4:3, then you don’t really know exactly what it will look like when you render the final version out in 16:9. In that case, you might want to set your project properties to a 16:9 setting so you see in the Video Preview window what your final render will look like.