Does anyone know of an online source for plans to make a flat screen tv built into the wall?

that's a really cool idea! i've thought about that and there may be a company with really skinny tv's, but nothing that will be built into your wall. If i were to do it, i would merely put a recess into the wall and mount the tv into it. I would leave atleast a little gap between the sides of the tv for ventilation, though.

You may be hitting a bolt, or other hardware, related to the fireplace. There is a chimney flue that runs up behind the wall there....and depending on how it was constructed, it may be made of stone, brick, or cement block (or it may just be a steel double wall pipe mounted with brackets to the structure) I'd suggest a couple of options... shine a light into the hole and try to determine what you are hitting, or drill some test pilot holes with a very small diameter drill bit, on either side of the obstruction (to see if it continues past where you want to drill) or to tear out the wall just a bit, to see what it is. If your tv is very heavy, you may want to tear out the wall just a bit anyway, so you can install a 2x6, or 2x8, horizontally, across the wall space, securing it to the studs. This would give you some room to move the anchors left or right, as necessary. Have Fun

It really depends on what tv you are going to use as to how far it needs to be recessed. Also if your looking for a way to hide the tv look at vision art http://www.solarshadingsystems.com/

And if you looking for a high end tv and want it to be small wait untill pioneer releases its new kuro tv. Its a 60" plasma and only 9mm thick.

If your doing this on your own the best thing to do is but a tv and flat wall mount measure how deep it is and go from there. Just remember you might want to include a temperature sensitive fan for cooling or figure out some way to get air by the tv so it dosent over heat.

Have you looked at Panasonic's Life Wall? It's much more than a television, but really, really cool. It's essentially an interactive system that allows your wall to become a television monitor, a computer monitor, etc.

The problem with your scheme is ventilation. If there is not enough ventilation all the electronics will fry.