50" Plasma will still only likely have a resolution of 1920 x 1080 - so it wont be super-high res.
The easiest solution would be to use an iFrame, with a bit of JavaScript (or even just a link with a target attribute set) on the bottom row. Alternatively, you could use JavaScript to make an AJAX request for each page, but that would get a little more complex.
Yeah, I know it won't be super hi res, however the websites that I want to launch in it are maximum of around 900px across and the user will be stood next to the screen so it should be big enough for them to read and use. I know I could use an iframe, however it's the maintain state bit that I need to think about the logic on.
Was wondering if CSS would do it with layers show/hide etc. or is that sort of stuff not used anymore?