You might take a look at this site http://www.mlin.net/misc.shtml
. Mike Lin has this little app. called "WindowSizer" that is worth a look.
I am not sure if it is appropriate for what you need it for, but I do know that it works on 21" monitors.
It actually does the opposite of what you are asking, by setting the initial size and allowing you to resize to a lower resolution. it's a very handy Web Master tool.
I'm just not sure if it can be applied to T.V.'s or not. Maybe it will get you pointed in the right direction.
Like any program, make sure you read all the info.
Hope This Helps,