My man "KBVP" is absolutly correct regarding the TVs and viewing areas. Each TV is different. The size of the picture can vary somewhat by either the tube or maybe the frame around the tube.
To prevent this most of the nicer NLE’s and DVD authoring apps provide a graphical reference overlay so that the editor knows where the safe zones are. For instance, I use Adobe Premiere Pro and that app actually has two zones. One is called the "ACTION SAFE ZONE" and the other is called the "TITLE SAFE ZONE". The action zone tells me pretty much that anything within that box will show up on the TV. The title zone shows me where I have to keep my titles, lower thirds and menus positioned so that they don’t get cut off on ANY TV. That’s how it all goes down. Check to see if your apps have a feature like this. I live by these guidlines.