You can close down the Inspector window when you don't need it to make the viewer window larger. The button is underneath the viewer window. Second one in from the right. I think that is probably the answer to your question. :)
http://upload.wikimedia.org/wikipedia/en/a/a5/Final_Cut_Pro_X.jpg
Basically my final cut has an inspector and my video preview things screen is small. How do i change it so it looks more like the one in the link?