Watching online TV streamed from my browser to PC and HDTV without browser annoyance

Hi all. Just found this site. Looks very promising. Please forgive me if I am posting in the wrong area.

I just bought a HDTV, and have cabling to connect it to my PC. I wanted to start watching online TV, streamed from my Browser, to my PC, and consequently to my Tv.

This works okay; my TV looks like a huge monitor. What I'd like to do is find some way to hide the elements of my browser / desktop so I only see the streaming content, and just have a black border all around it. I haven't really found anything that can do this.

What I was thinking of, is some sort of PowerPoint Presentation window (or something like it) that I can run. It would cover the entire screen except for a configurable window in the center of it, allowing me to see the content that is running behind.

One thing I have tried is using a utility (powermenu) that makes the browser opaque. This works for some websites (the stream doesn't disappear), but for others it doesn't.

Does anyone have any ideas that may help me? Thanks for your patience